I think you're on the right track, too, but I'd also suggesting using the marlin spike hitch and ditch those heavy biners...
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Those biners might not be all that heavy...and after having already fallen once, the peace of mind knowing you CAN'T slip up over the knot and hit the ground again might well be worth the slight weight of a couple of quality lightweight climbing biners. It is for me at least...
Diygearsupply actually has some 4-5KN 'biners that will hold ~1100lbs on the spine...
they only weigh .85oz each. Not too bad really.