the trouble with you, nym, is you set out to make a track in it's own right. what i'd do if i were you (and i've never worked with a vocalist, rapper or otherwise, so my opinion probably means sheeyat) is make a basic beat, no more than a basic loop with a couple of changeups to give them a bit of variety, enough for them to 'feel' the track, and then get them to record their vocals on that.
then, and here's the clever part, using your standard track-making procedure, you work the basic blocks you made originally AND the vocals into a track in its own right
at the same time. that way they should mould effortlessly into one artwork (hopefully) and both you and the emcee get what they want. plus you give them a little surprise in that they'll hear a much better track than the one they rapped to. this may make them spread the word about our lord antonym h. christ (reffering to the other thread about thew da vinci doo doo, where you said you hope you weren't related to jesus) or they might just pee a little.
hope this helps.
