The player stats on this site don't go into "minute" detail but the appearance data gives a good indication that you're barking up the right tree.
Rory McAllister - 15 starts + 47 sub (so 76% of appearances were off the bench)
Shane Sutherland - 27 starts + 63 sub appearances (70%)
Tony Low has a more extreme ratio ratio, with 2 starts and 17 off the bench (89%)
But then there are other players who never ever started, but made quite a few appearances - Agdestein (16) , McMillan (11), Fetai (10), Wee Deano (7), Ibra (4).
Sadly none of the players mentioned ever did anything to earn the title "supersub". With 63, Shane actually has more sub appearances than any other ICT player, although Nick Ross is catching up with 60 (but has 104 starts).