I'm not sure what the statistics are regarding whether 2nd rowers suffer less from knee injuries than outside backs but regardless of this the suggestion is not a bad one. We've struggled to find a right sided attacking threat in the back row and Manfredi would certainly offer that without losing anything in defence.
That said, for my money he's the best winger in Superleague when fit and, provided we could get him back on the field for an extended period, I would always want the best players in their best positions. The big caveat though is the 'if'. If it's terrible luck then, as Lomax is currently showing, it needn't follow that it will keep happening, even if that appears to be the case at the time. However if it's something else (like the generic weakness mentioned above) then that's a different story and if moving to 2nd row would keep him playing I think that would benefit both club and player.