Hi Chugsy, I got your PM but thought I'd reply in here in case others can expand, or indeed correct, my info. I've not used an SRAM derailler but the beauty of bar end shifters is that they can work indexed or on friction. I have the Dura Ace 9 speed indexed, but a simple turn of a part and they become friction, the front derailler is friction anyway. Worth chatting up a frinedly local LBS mechanic, these guys love a challenge and amazing what they can manage from the 'spares' box. but there are other ways of doing this, you'll find some pics and extra detail on my Flikr account, all used to be on here but got lost in the forum upgrade:-
http://www.flickr.com/photos/37729119@N08/sets/72157623073074209/
I have my twist shifter mounted at the end of the drops, there is an official thing called a Hubbub adaptor to do this but it costs £40. I got an old flat bar from the bin at LBS and cut off a piece of the length needed to take the shifter, it had an internal diameter of about 19mm. Then I bought a 19mm to 19mm(3/4") connector for joining plastic hoses, got it from a Koi Carp supplies place online, less than £2. Belted one end of that into the bit of straight bar with a club hammer, it peeled some plastic so is never coming out. The other end goes into the end of the drops, my LBS mechanic sorted out an expansion bolt fitting for this for me so that it's easily removable. As I use Midge bars the drop area is very short so I didn't cut any off, you may want to shorten the drops for yours. I think I spent about £5 overall and it works very well, actually easier than a bar end shifter.
Another alternative is to buy a Thorn accessory T Bar, this is like a mini handlebar that fits to your stem in place of some spacers and gives you mounting space for bits including a twist shifter. I've seen this as a solution for a rohloff with drop bars. I think they're about £17 each though. Also I don't know if this would work with your folding setup.
Yet another is not to rule out trigger shifters, I succesfully reamed out the inside clamps on a set of 9 speed shifter pods so that they'll fit round the bends onto the tops of drop bars. Obviously this sort of thing is entirely at your own risk
I just used some largish metal files and a bit of elbow grease, 30 mins work
There are other, more expensive options, but for quick, easy and cheap then the home made bar end adaptor for the twist shift takes some beating. Re the bar end shifters, if I was doing them again then I'd buy a pair of 'thumbie'(
http://www.paulcomp.com/rdthumbie.html) mounts. These are a bracket that fit on the top of the drops near the stem and then the bar end shifters slot into them, sideways, rather than end on into the bar ends. With the bar end fittings you can't really shift from any regular ride position. It's just about doable from the drops with heel of hand and last couple of fingers but still normally involves some movement of your position. With the thumbies you can shift from tops, corners and, if your hands are large enough, from the hoods as well.
Let me know how you get on and if you need any more detail on anything. I'm certainly no expert, the quantity of information is more due to my mistakes than any knowledge