So we need to beat UT by a few points as possible?
If it gets to scoring differential, I think
y=2x-2 is the formula, where
x is ISU's margin over UT and
y is the margin that UT can beat BU by and still allow for ISU to win the 3-way tiebreaker. The minimum ISU margin over UT would have to be 2, though.
That would leave ISU and UT tied on points, with BU out. ISU then beats UT on head to head.
So if ISU beats UT by 7, UT can beat BU by 12 and ISU still wins the tiebreaker.
If ISU beats UT by 10, the UT/BU cushion grows to 18.
....and so on.