>>1750059that is a handsome shitter
clamp on a bottle cage
you can just do it with hose clamps which are next to free from an autopart/hardware store
do 1 round of tape under them and it won't scratch the frame even.
generic metal bottle cages will fit larger bottles like that too if you just bend them open a bit
lose the light if it doesn't work.
and get some better brake pads or atleast set those ones up better.