I am working on a project which contains EZKeys and Addictive Drums 2. Before adding audio, I'd like to add random small variations in tempo, so instead of it the project being a strict 100bpm throughout, there's a degree of humanising. I know how to do this within AD2, but how would you do it at project level? I'm particularly aiming to make EZKeys sound less mechanical.

Thanks!

Open up the tempo view, zoom in and start drawing suble tempo changes. Tempo changes can really add a human quality. If it's a keyboard part, you might try adding the Quantize and playinging around with the Swing to help give it a slightly more human feel.

I would recommend enabling snap at no less than a 1/4 so you don't generate hundreds of unecessary tempo changes - maybe even just at measures.  Too sudden changes within a measure will just make the timing sound 'wonky' rather than human. Humans tend to speed up or slow down gradually over several measures or going into and out of choruses/bridges - unless the piece is really intended to be rubato, in which case it wouldn't usually have drums.
 
If the piano part was entered in the PRV rather than recorded as a live performance, 'humanizing' velocities and durations will probably be more important than varying the tempo.

This is dirt simple when everything is still MIDI. 
Find the place in the timeline where you want to insert a change. I usually do a BPM change at two bars before a section change (verse/chorus), then another BPM one measure before. I'm pretty sure it's under Project in the menu, it's not EDIT like you think it would be. Anyhow, in there is an option to "Insert Tempo Change". Enter all your info and BAM! 

I do that all the time in Tempo view. Very simple when everything is MIDI.
 
What I would really love is the possibility of using a CC (like Mod Wheel) to alter tempo and record the changes in real time as the music flows. Pretty like a conductor would do in frot of an orchestra. Don't know how complex that would be to program.

The tempo map is really pretty primitive. I suggested to automate tempo with CC1 events a while ago, but I don't think it was considered important.
 
 

The Fit to Improvisation technique is something very useful too.