Hi Jon, here's my two bits.
I would forget about a harness system. I know that AIDA has been talking about this kind of thing with a guy at the surface with a reel, which MIGHT work in up-down constant ballast training, but i think that the risk of entanglement is too high.
Now, this will depend on the visibility, but all you should really need to do is throw a weighted line in at one corner of the hole and tie it off at the surface to something. Breath up on the ice, then slide in like a seal, follow the line down. When you get where you want to be, either the bottom or somewhere on the line, then have a look up. You'll know from scuba diving before that the hole might be indistinguishable from the surrounding ice if it's been cleared properly, but the line should be highly visible. For those that don't know, lakes usually have their best visibility when they're frozen, so you should be able to slowly venture away from the line, looking back every few feet
The danger is not when you're deep: at depth you can see the hole's area and the line. The danger is when you are right up against the ice....at this vantage point, it's easy to lose sight of the hole. Just make sure you can see that descending line, and you will always make it back to the hole.
Have fun my friend, just don't let your wife, girlfriend, or really anybody see you take those wetsuit bottoms off
Cheers,
Erik Y.
