I am surprised that the company could block the sale. Usually they can't just block it, they have a right of first refusal which is where they have to buy it from you at the same price that's being offered.
I don't know if it has a specific name, but I believe it is possible to work around the company in cases like this. You basically setup a contract where you accept money and then agree the transfer shares as soon as they become liquid. No transfer of ownership happens beforehand so the company is left out of the process entirely.
I have never tried it, but I always thought it was an interesting concept since I first heard about it.