Even if you just somehow circulated it around the water pipes of the washer to keep them from freezing up, that would be good. Of course maybe there aren't a lot of people who have a poorly heated laundry room like me.

It's not a switch on the dryer per se, but a functionally equivalent product exists. Indoor/outdoor vents allow selection between venting the dryer inside through a lint trap or outside through a normal vent.

Mentioned here: http://www.lib.niu.edu/ipo/ic020718.html

It is a very interesting idea in theory. However, you have to be really careful when it comes to indoor dryer venting, as there are significant safety and litigation issues involved. Dryers emit a large amount of moisture which can lead to water damage, mold, mildew and other problems. The vented air also contains considerable amounts of lint, which is a fire hazard and can also cause breathing problems. It would be very important to fully filter out the lint. The indoor lint traps you see in hardware stores do not trap lint effectively and are actually a code violation.

There are products exactly as you describe on the market already. I bought a kit at Canadian Tire for $9. Here's a link to the manufacturer's site:

http://www.dundasjafine.com/products/ventkits/heatkeeper.html

It has safety mechanism that negates any danger of blockage from lint (although cleaning the lint trap on the vent and the dryer is very important). Also, the humidity coming from the dryer is welcome, since it'll be during the dry/cold winter that you'll have the vent turned to blow indoors.

Sounds good, except that unless the exhaust is ducted to far away from the dryer you'll be sucking in the water you just removed from the clothes ;) It's in vapour state, but it's still there.