One handed trills?

[Iwhaiwnfi]

I've been playing for 4 months, and I still can't seem to get this down.

Trills (two steps going back and forth at a quick pace) are very difficult to do one handed, yet I've seen videos of people FCing songs with repeated trills. Is there any special way to do it, or were they just playing two handed?

I'm specifically talking about very long trills, such as in Max Forever. The up and down trills are probably the hardest.