You're a brave soul. The only advice I have is to take a page from CPR and run an airline from the top of the siphon to a powerhead. The powerhead creates a constant suction on the top of the siphon that removes any accumulation of air in the siphon. RVT designed powerheads generate more suction.
It's not the big gulp of air that kills a siphon, its the accumulation of lots and lots of small little bubbles that build up inside the siphon and eventually cause it to lose flow.
The siphon simply can't fail. If it does, you'll have a flood real quick.
You might also consider a float switch in the system somewhere that could detect a siphon failure condition and kill the return pump fast enough to prevent flooding.
I'm with you....I didn't want to drill my tank (let alone drain it, in order to drill it). I went with a CPR overflow and have had no problems with it.