The local Home Improvement center might have the diverter/filter you need. I'd
only do this with an electric dryer though.

It's a plastic box you connect in the hose, with a flap and a handle to choose
where to divert the exhaust to - inside or outside.

The "inside" outlet connects to another hose which dumps the warm moist air
into a little container which has a fine lint filter and water on the bottom.
Microscopic lint is trapped when it hits the water, and the warm moist air
skims across the top of the water and out while passing through yet another
nylon-stocking type filter.