Do you want to learn the arrangement of the original Broadway cast soundtrack? Or the famous 'hit' version by The Fifth Dimension? Both are quite a bit different. If you want to learn the original(and in the same key?)you're in luck as the bass is panned to one side of the mix(something that was done in those days). Check it out... http://www.youtube.com/watch?v=tB90kgSnqFE
Just play along with the side without the bass...a crude "music minus one". Recorded over a year later, the 5D version has the bass square in the center of the mix, but if you have the time to study Joe Osborn's basslines, it's a master class of iconic playing, especially the 'Let the Sunshine In' coda... http://www.youtube.com/watch?v=kjxSCAalsBE
Other than that, you may have to search far and wide to find true 'music minus one' instructional material for that song; can you get with a guitarist who could learn the arrangement you need and rehearse it?