P19 is clear that the option to place the BUA without dicing on/adjacent to a road is only available for a BUA not on a hill.
"If on a hill, it is placed when the hill is placed... If not, ...(a) astride or in contact with a road..."
Furthermore, if placed after a road that itself must have been placed after the hill, it would clearly not be being placed when the hill is placed.
Also on p 21, it is specified that a BUA placed after roads in the sequence is "BUA unless on a hill".
So there are multiple reasons in the rules why you can't do what Lawrence (Ho) suggested.