I have an idea... since the IceProbe works best when it's insulated... why not replace an HOB filter's cover with styrofoam and put the probe through that? Insulate the rest of the filter with styro too.... Just an idea.
With sufficient water flow thru the HOB filter, there is no need for the insulation since there is little temp difference btw the water in the HOB and the tank water.
I dunno, I read a post where a guy's probe brought the tank down 2 degrees until he insulated the HOB, then it brought the temp down even more. Well, it never hurts to try, right?
Find the difference in temperature of the water in the tank and inside the HOB filter, and you decide for yourself rather it is worth doing. Yes, it won't hurt anything.