I'm not using them on my folder, but I used these
for the derailleur and these
for the rear brake on a bike that I set up for handlebar interchange. (Loosescrews has the sets for handlebar interchange, but the links above are for splitting cables to pack/fold a travel bike.) It doesn't say on the Loosescrews website, but the set that I got turned out to be Moneran Cycles Quid Pro Quos, which so far have worked pretty darn well for my application (see flatlander's link to sandsmachine.com above for info about different cable splitters).
Just keep in mind for any splitter you get, you'll need another set of cables to finish the job. And as Jur noted above, you need to split a section of bare cable without any cable housing.