You could save yourself a lot of headache by using 4 tracks and just keeping it that way.
You COULD use a track for kick and snare.
Then, do a "submix" of your toms and overhead mics to two tracks. You need to of course be very careful about mic placement in this case. Make sure that your toms and sounding the way you want....etc.....
Trying to do 3 mics like suggested earlier is a great idea IF you have a great sounding room. If you are dealing with your normal ol' "plaster and/or drywall" room, with 7-9' ceilings, and no treatments to balance RT times in the room and kill low mid phase cancellation, well, I can assure you that your overheads you would use in a 3 mic setup are going to sound very odd. The bad room IS GOING to create comb filtering on the overhead mics, and the resulting sound will be rather dull and inaccurate. This is a ROOM PROBLEM, NOT A MIC PROBLEM.....You can move the mic's all you want, and with a LOT of attention to detail can move the phase cancellation problems (these contribute to the comb filtering effect on the mics...) to a low frequency, but I can assure you that you will never get phase cancellation to a low enough frequency in a bad acoustical environment to be able to have a good sound with ambiant micing (that is more or less what a 3 mic setup for drums is.....).
You can however move that phase cancellation down low enough to where you can use your overheads for more of the "top end" in the sound. But, you will need close up mics now to compensate for the lack of low end the overheads will provide. On Toms and even the Snare in many styles of music, that low end is of course important!
Hmmmmmmmmmm....I can tell you straight up, if you can't get a good demo recording out of 16 tracks, you are probably having many OTHER problems with your recordings. I seldomly use more than 16 tracks for anything other than bands I record that will be distributing this recording via music stores, etc.....and have a pretty good following.
If you have grand designs of "double tracking" many guitar parts, etc....you might have much better luck bouncing those tracks than you will trying to economize on your drums. Drums are important in a mix, and they are also very hard to deal with in a mix. So, it stands to figure that you will want the most versatility while mixing them. You have NO WAY of knowing how to mix your drums ahead of time to try bouncing them all down to a stereo mix and have that mix hold up well for the rest of tracking/mixing. You should looks to cut down on tracks somewhere else.
Good luck.
Ed