I would probably go with the Option and an approval to do the work.  Possibly under a Lease where I pay rent while undertaking the work.  You can then assign the Option to a new buyer and this will save you paying double stamp duty.

I'd also suggest you source what I call a "blind option" so that your new buyer can't see what you optioned the property for, i.e. your Option needs a "higher price" clause.

Cheers,  Paul