With Test Lion Lee Byrne out injured, Wales coach Warren Gatland is thought to be considering playing fellow Lions Leigh Halfpenny or James Hook in the No15 shirt, but JPR has other ideas.
"I would play Jamie because he's got considerable experience at fullback, has got the size and strength, and is not going to be threatened by the high ball," Williams - arguably the world's greatest ever exponent of full back play - told the Western Mail.
"Don't get me wrong, Jamie had a great Lions tour, but people, starting with New Zealand, are going to be watching and attempting to man-mark him out of games.
"It's what happened against England in the Six Nations last season when Joe Worsley marked him out of it.
"Teams know now what to expect from Jamie. It's his second season at centre and it's going to be harder for him.
"I think we have seen that already with the Blues."
Roberts began his professional career at full back and on the wing before moving closer to the action last term and JPR feels the extra freedom could make him even more dangerous next month.
Wales take on the All Blacks in the first of four internationals on November 7 and JPR believes playing Roberts at full back would give his countrymen an extra edge, even if he still expects New Zealand to come out on top.
"With Lee being out, it gives Wales a chance to use Jamie elsewhere," added Williams.
"Being at fullback would given him the option of entering the line in different places, which I think could be quite effective, and at pace.
"He would be harder to stop and my choice to fill in for Lee against New Zealand.
"I don't want to rock the boat, but I don't think we will win against the All Blacks.
"But, to give us a chance, Gatland must make the right selections."