Why not use a sailplane/hang glider etc. in a rising air mass as an example?
If you launch into the wind from a ridge, you can gain potential energy (i.e. climb) - just as if you were a powered aircraft. Ditto in a thermal, or wave soaring.
I even read an account of an old KC-97 with a pilot who was glider rated - he found a nice mountain wave, pulled power back to idle, and climbed!
Does the rising air mass affect the L/D? The answer is NO - even though your
apparent L/D approaches infinity or beyond.