No chance of a quick job on a heavy here! Best you'd get is 737-size. The CAA reckon, and I'd have to agree, that flying FO in a medium jet is less demanding than flying single-pilot in a simpler aircraft. Hence the absolute minimum 700 hours to operate single-pilot IFR public transport, commonly raised to 1000 hours by the terms of the AOC. That is why no-one in Europe flies air taxi to build hours.
I know someone with a command of a multi-crew N-reg jet without any significant previous multi-crew time. It isn't heavy, but still I know he was way out of his depth when he started, far too reliant on his FO. The whole point of keeping people away from command until they have some time in a similar environment is to avoid the Captain being in that situation, as far as I can see. I don't think a flight test could replace that.
I have 900 hours, including 300 instructing. I have flown some complicated machines, just as difficult as some multi-crew. I have flown a jet-transport sim (the real thing, BA's 767) and as an FO, with the normal training, I could do it with no problem. I would not like to command anything of that speed or complexity (and some bizjets are as involved to fly) without some fundamentally different experience behind me.