Syncing Up Audio

Hi there,

I'm doing an assignment at university and my idea is this:

I have a 4-beat backing track and need to loop it: this is say 140BPM.
I have a vocal track of a song that is perhaps 138BPM.

Without using elastic audio or time stretching in a different piece of software, is there a way just using max objects such as the phasor~, groove~ object etc that from ONE toggle/bang I can get the backing track music to loop and the vocal track to play over the top but so they are in time with each other? It's basically a mash-up (Girl Talk if you know of him) so that in my work for example i'm running Carly Rae Jepsen over the top of Jay-Z/Kanye West.

I also need it so the sound files are PRE-loaded into the patch without having to do it yourself as an end user. I must have pre-programmed everything apart from a maximum of three buttons/dials/knobs to change things.

Any help is greatly appreciated!