In my opinion, and experience, a planting hole over 24" deep is just not worth it. However, I shared your enthusiasm for depth once. I brought a tractor in, put on an big auger, and bored down. Only problem is I hit a deep water line the first try and busted the deep sewer line the next hole. Every time I over-do it something messes up.
Before I'd do all that elaborate stuff, I'd just get a discarded 15-30 gallon nursery container, stick it in the ground, and fill it with nothing but good compost or the stuff you can buy such as peat, potting soil, top soil, etc. It's really very simple if you let it be. At least I keep telling myself that. :wink: Next time you pull up a tomato plant at the end of the season you will be surprised at how small the root ball really is.
Good luck, but be careful with the heavy machinery!
Don