Aucky,
I appreciate your desire to make use of the opportunity you have. Re: the EC135 (apart from police machines with dedictaed systems), the EC135 is not a normal filiming machine. By comparison, the AS355 is standard kit where a twin is needed. All the mods and kit are already cleared and available.
The main problem is that EC135s will be shiny and new, and their owners not wanting to risk the paint job for a utility job.
Because it is not used much in the role many of the wrinkles have not been worked through here in UK/EASA land. An example is BS's issue about Vne with door's open (assuming you will need the doors open), I am trying to remember what the kit consists of. I think it was a sort of leading edge kit for the front of the opening where the door normally goes. My guess is that it would be expensive and you would have to buy it and get it fitted.