4QD.co.uk makes relatively small brushed controllers (like the 4QD itself) that support regen. I don't recall if the 2QD (even smaller) will do regen as well. They won't be cheap controllers, though.
As Fechter notes, a freewheel will help; adding this could be mechanically complex depending on your system's specific design. If the wheel doesn't have a place for a typical one, but the motor shaft is a common type, you can probably get a sprag clutch that will mount to it that you can then mount your output sprocket to (or even a prebuilt sprocket/sprag (sprague, roller) clutch unit).
And also as he notes, if you really want to increase the range, simply changing from SLA to a good-quality Li-Ion pack that's made of new, matched, brand name (samsung, LG, etc) cells intended for high discharge rates (unlike the stuff that cheap batteries are made from), that uses a quality common-port BMS (like JBD), will do much more than regen could.
Regen *might* get you a couple of percent of your power usage back over a ride, but since the charge or discharge efficiency of SLA isn't that great, you don't even really get that much.
SLA might get, at best, half the capacity it states on the label for EV use--usually less than that, and if it's not kept charged all the time it will degrade (sulfate). Lithium will give nearly the full capacity, and lasts longer the less time it's fully charged.
