"Who is in charge of updating Cockney Rhyming Slang?" was Stan's question. With outdated references such as syrup of figs (although someone's grandmother apparently swore by it) for wig, Ruby Murray for curry and even Alan Whickers for knickers, sometimes Rhyming Slang seems to be from my grandparents' generation. But it's part of a living dialect and does get updated. It's a good question, which I will now fail to answer several times.
1. No one
It just happens. One day flares are referred to as Lionels. The next, some bloke becomes Prime Minister and they're Tonys. Popular things that rhyme are obvious and just get made up all over the place. Because they're obvious everyone who uses the slang figures it out and picks it up. End of story.
This version of events ignores several factors, including why it's known as Cockney rhyming slang.
2. The population within the sound of the Bow Bells
The traditional definition of a Cockney is someone born within sound of the Bow Bells of St Mary-le-Bow. More usually it refers to working class East End Londoners, who speak with a distinctive accent and feature rhyming slang.
Under either definition Rhyming slang begins in East London, presumably in the pubs and workplaces. There, the classic cheeky cockneys with their cliched wit and eye for the main chance while away the hours trying out new slang on each other, always trying to keep their dialect one step more confusing to those not so blessed as to be born in London.
A problem with this is the interconnectedness of modern life. In earlier times many references obvious to Cockneys would be obscure to outsiders (and vice versa). Many modern slang words reference events and people that are nationally and internationally famous, so rhyming slang is not so much obscure as an affection. Of course this may have always been the case. However with the rise of working class cool over the last 50 years, it's an affection that has spread beyond it's origins, which is why this site allows you to rate slang as classic, modern and "mockney".
(The pub theory does help to explain why there are so many rhyming slang words and phrase for urination.)
3. Mockneys and Estuary English
As a nice boy brought up in a secure and comfortable middle class family in a small town in the home counties, I obviously attempted to ape working class urban speech as much as possible. London being the closest metropolis my accent is probably closest to Estuary English. As might be expected, when I lived in London I picked up quite a bit of cockney slang making me that most despicable of creatures, the Mockney.
The traditional East End Working Class roots of rhyming slang acknowledged, modern versions acquire their references from popular culture. Those of us who have grown up speaking a cockney influenced language and are equally part of the popular culture make up our own slang terms. In addition, Cockney culture is now part of popular culture (and arguably has been since Dickens, and certainly from My Fair Lady) with one of the most watched TV programs being Eastenders.
But wait! Am I really arguing that rhyming slang is being invented on television, like here from the 1 minute mark? I've clearly gone a bit Pete Tong.
4.All of the above, maybe
I may know more than when I started, but I'm at least as ignorant of the actual answer when I started. Like many things in language and popular culture, even if you can identify a particular starting point, the way it spreads and how it becomes accepted is unclear. So Stan, if you want to update rhyming slang I guess you'll have to get on your Dick Van Dyke and have a go yourself.
 A laxative, still available but out of fashion.
 A famous singer of the 50s. Here she is singing a Johnny Cash song, which kind of surprised me when I discovered it. It turns out this was when Cash's career was taking off and Murray's was slowly declining. Also, it was still the period when the song was as important as the particular recording, so British and Irish singers would often pick up American songs (and vice versa) and make them part of their act.
 Referenced in the nursery rhyme Oranges and Lemons
 Also some Mancunian leading to such horrific constructs as "Let's have a butchers, our kid".