Adding an aluminium stay to a frameless pack

After buying 2 new backpacks that don't work for me (
), I'm looking at modifying my old GoLite Pinnacle. It's been a great large day pack, but hasn't worked even for an overnighter for me. In spite of careful packing and trying a bunch of things, I can't stop the foam back pad from sagging and bulging into my back in the wrong places.
I have 2 aluminium stays from a defunct pack that was very comfy. My more recent old pack only had one stay, in the centre of the back, which worked well. Sooooo, I'm considering trying to attach a stay to the centre of the back pad somehow. The pad sits very snugly in the back pad pocket, so any other fabric I add would need to be very thin.
I have some SILnylon - unnecessary in terms of waterproofing, but the slipperiness might help me get it back into its pocket. I wondered if I could make a 'pillowcase' type of thing, with an extra sleevesown sewn
onto that for the stay to go into.
I also wondered about trying to glue the stay onto the CCF back pad, to save space. But I'm not sure if that would work (I'd probably only have one chance to get it right), and I'm not sure what kind of glue to use.
Do either of these sound reasonable, or does anybody have any other ideas about how to do it?
Thanks for your thoughts.

I have 2 aluminium stays from a defunct pack that was very comfy. My more recent old pack only had one stay, in the centre of the back, which worked well. Sooooo, I'm considering trying to attach a stay to the centre of the back pad somehow. The pad sits very snugly in the back pad pocket, so any other fabric I add would need to be very thin.
I have some SILnylon - unnecessary in terms of waterproofing, but the slipperiness might help me get it back into its pocket. I wondered if I could make a 'pillowcase' type of thing, with an extra sleeve

I also wondered about trying to glue the stay onto the CCF back pad, to save space. But I'm not sure if that would work (I'd probably only have one chance to get it right), and I'm not sure what kind of glue to use.
Do either of these sound reasonable, or does anybody have any other ideas about how to do it?
Thanks for your thoughts.