Jason,

Yeah man this is a drag! There are really only 2 options for you if all you've got is a 21 fret guitar.

The first one is to play the highest lick an octave lower. The problem with that is that the whole point of this particular lick is to ascend all the way up the neck. So I can see why this approach may not sound good.

Here's what I recommend: when you get to the C note at the 20th fret of the high E, go for all the higher notes using bends from that fret. For example, a full step bend on the 20th fret would give you the D note, and a step and a half bend would give you the high Eb note.

The only lick you would have to alter is the bending pull off lick. Forget about the quick pull off, and just bend up a step and a half to that Eb note in place of the pull off.

So to summarize: anytime you need to hit the 22nd fret, just bend a full step from the 20th. To simulate the bending pulloff lick at the 22nd fret, bend up a step and a half, then finish off the phrase with a full step bend, then back down to the C note. Make sense?

Hope this helps! Cheers!
Mike