...I was offered the option to pay for the 51% (not just the 49%) of an aircraft build so I know there are ways round the rules.
I am puzzled. If a prospective owner of a HX50 isn't inclined to put 51% effort into the build, can't they just arrange for someone else so do so on their behalf? That would be no different to an E/AB aircraft being built by an original owner and then being sold to a new owner some time afterwards.