Aftertouch

The aftertouch is a little tricky to engage--you need to find the right spot and a lot of pressure (you may need to bring in an extra finger to help). The sweet spot seems to be a strip along the keyboard aligned with about the center of the white keys or the ends of the black keys. An easy way to find it is to press down at the end of a key and then slide your finger up till you hear the effect. The default synth patch (483 Classic Saws) is one you could use as a test; aftertouch should bring in vibrato.

It's not as useful as on a keyboard with more sensitive aftertouch, but it can still be handy in some situations.