Map the face buttons to both the right stick and face buttons. This makes the right stick a digital input, but the left stick is still analog. Therefore, only use the left stick for finite adjustments, and un-train your brain from using the right stick like an analog.
Then, either get used to double tapping left/square to turn, or figure out some way to macro or some shit. Same goes with the boost, though it's still similar to regular katamari controls. L/R don't really help much, just ignore them. I played the game on Vita and had a better time, but I'm sure it's just as good on PPSSPP
And enjoy the game, it's certainly not better than the console titles, but the levels are relatively fun and don't get old. Don't forget to do the special stages (on the sand island)