Granny chargers are perfectly safe well reputable brands (I know you were joking but someone will go off on one), I used one for 6 months due to BP at the time making a mess of installing a charger. I sold my MG one recently actually as it happens.
I would email the CEO office and see if Motability would help out they have discretionary funds. You could try other places but knowing these people it’s highly unlikely they will do anything for car related stuff like that as it’s just not inside the remit of these schemes. Even a disabled facilties grant wouldn’t cover an EV charger. I think these best bet is to plead the case with the CEO office and beg for help, what’s the worst they say no and they seem to be a hell of a lot fairer than the phone script monkeys. When the standard phone guys said I would lose the hire car and they’d leave me without a car until my Enyaq arrived and not only that it’d take 6 weeks to get my PIP money returned too, CEO team immediately reversed all that and promised to keep me in a car until mine was ready, after the normal phone guys and directline had told me nothing they could do…
Yes on the face of it Motability aren’t responsible here to fix this but it’s just possible with a little pleading for help they may.