Now, I'm not 100% sure about on these Hyundais (new to the cars, just picking mine up in a week or so), but on other return-less cars I've dealt with in the past, if you want to add a fuel-pressure-regulator, you have to add a return line to your fuel system...

In most cases this means getting a custom fuel rail, and you run a line from the fuel rail (through the FPR) to a little piece that you "splice" into the fuel line...

I'd imagine the same would go for these, but if I'm wrong someone feel free to correct me

 

correct, but you dont need a custom fuel rail, one from a 1.5L sohc will work along with the tibs an elantras.

 

on the Accents with the returnless system, you'll fing the regulator is in the tank! (pretty stupid I know) so just swap that one around with a malpassi or something similar, but if you want to go hardcore, thats when you'll have to do all the running of the return line back to the tank, moving filters and regulators into the engine bay...