Just take him yourself. First time you enter you get a warning letter, you then get twenty eight days, in which you could drive in every day before you get fined! Simples!
And ALL the LEZ rules changed and got more stringent. Practically EVERY blessed vehicle has to pay! Think the only exceptions are pedal cyclists lol!
You MUST pay before you drive in or straight after or get fined - simples!
Sad to say people obviously took advantage of the 'loop hole' before but now it's slammed shut! Someone at the yard went to patchetts but went in the wrong way after getting lost (don't ask how seems OH and sat nav went wrong)
They got a massive shock after christmas with a massive fine and even after taking legal advice they have got to pay it as LEZ has been WIDELY advertised etc etc
You could try Brad at Bicester Horsebox hire. He has small self drive 3.5t boxes,which are possibly exempt from the LEZ. Google Bicester horsebox hire.