You could use a brushed ESC with a servo tester to relace the receiver:
The only issue with this set up is that the ESC has a fixed low voltage cut out at 3V per cell, which is lower than you would really want to go. You might be able to find a brushed ESC somewhere that has programmable cut-off voltage.
Or maybe someone clever could design a simple circuit?
EDIT.. Oops.. I see you intend to use a 6s battery, that would be a problem for the ESC I listed because it's 3s max. I dont think you will find a 6s capable brushed ESC.