OK, I'll take a stab.
I'd go for a "hybrid" ridgeline tarp/rainfly. Shape the back (closed) end like the tent but leave the door-end extended like a tarp. Use a hiking pole to prop it up to create a covered porch and give you a little ventilation.
The 1.1oz weight is for a square yard of material, not running yard, and it's also the base material, without the silicon, finishing, seam sealing, etc. I think you'll need 5 yards of fabric (running yards for purchasing, that is.) And I think the finished fly will be in the 8-9 oz range (without any lines or stakes.)
That said, you could just take a basic flat tarp with you and set it up over the tent.