You have no clue, what I've done..

If you want to try it out for fun or as a learning experience, then all the more power to ya!
(pun intended)
Just realize that given best case scenarios, you're not going to be getting the results your wanting.

People told me I was nuts using a 12v 60Ah battery to power an inverter to run a 36v charger to charge a 36v 10Ah battery while using my ebike.
I am nuts!.. And, like you, I had the equipment already and no funds to buy an additional battery, so it worked out well... it's inefficient as he'll, but it definitely works and effectively doubles my range although I'm using 500wh of energy to produce 360wh extra..

Let me get you the details of my setup...
(Borrowed from one of my posts on another site)

1.) 12v 60Ah line for accessories.
(12v-30a fuse on positive side going to main accessories line)
Which by the way is also connected to a 200w inverter that has a 36v charger connected to it so I can charge my 11s battery (#4) "on the go".

2.) (same 12v battery)/12v line, inline, with a "33v" battery, setup on a switch to go from 36v to "48v".
(12v-30a fuse on positive side going to switch).

3.) 24v battery (2 SLAs) in series with the (same) 12v battery/line.
(32v-30a fuse on positive side going to controller - [controller draws less than 30a - technically 20.9a max])

4.) "33v" battery (11s LiFePo4) on aforementioned switch (see #2 above).
(32v-30a fuse on positive side going to controller - [controller draws less than 20a - technically 17.6a max])

P.P.S. After my first 2 years of using/building e-bikes and blowing countless controllers, chargers, batteries, etc... I've learned to fuse ANYTHING that can short out!