Paul the "V" of the belt would NOT be upside down on one of the pulleys at all. If you took one of the belts, and twisted it to make a figure 8 the "v" would still be the turned the same way on each end. Just like you buy a bandsaw blade all nicely coiled, but the teeth are all the same way. We used to do this on shop fan motors to reverse the fans for pulling air in, or when smoke in the shop became unbearable, to push air out. In these instances we did add an idler roller to keep the belts apart where they crossed by putting a little side pressure on one of them, but we were running these for HOURS, not just a few minutes, and sanding on a VS is at slow speeds anyway. SO IT WILL WORK! Yes, you would have a friction problem, but if all you were using it for was sanding, you could get a lot of use out of it before it parted or broke. I stated in my previous post that you would need a slighly longer belt for the reverse operation, but you would use a standard belt for the forward operation.
Rob