Slot the firewall for the up and down motion of the push rod sleeve, drop back about an inch or so on the inside of the fuse behind the firewall..install a balsa piece from the fuse side to the push rod sleeve and glue the sleeve to it...should take care of it..
That short of a distance with just the rod sticking out of the sleeve to the carb, their will be no undue flexing..
I had to do that on all my 4strokes...when I had some..