Don't think it will fit in the OE brackets, but another option i've done is to stick some velcro on the bottom of the changer and some on the top of the sub in the rear access panel and slot it in there. Don't know about you but if someone is going to nick it i'd rather they pulled at the velcro than ripped the sub to bits doing it, cos lets face it if they want it, THEY WANT IT!
I got my sticky velcro from Halfords, i think it was about £2
Good luck
Lewy