Not for long.
Will a 3.50-4.00 x 14 tube work in the rear tire?
Maybe if you use a pair of them.
A 5.50-6.00 x 14 might work OK, if such a size is even available. I am in need of a rear tube myself. But I cringe at the thought of asking how much they go for at the dealer, considering the extremely limited applications for that particular size.
That's actually a very ingenious idea. The obvious advantage would be that you could ride the bike home after the tire suffers a puncture, because the likeliness is high that only 1 of the 2 tubes would get punctured!
But the issue that would need to be over come, is how to properly address the dual valve stem situation.
www.americanmototire.com has the OEM Bridgestone 180/80-14 tube for $21.41 including shipping to the 48 contiguous states. They have a variety of tubes suitable for the front ranging from $15-30. Be sure to account for taxes and shipping when comparing costs--some suppliers nail you with shipping and handling charges.
The dealer had the rear tube for $10 bucks.
1995 Yamaha TW200
1983 Toyota PU
2002 Suzuki Grand Vitara