Yeah, no question - that's why I was saying, if that pin is already connected to the CPU... if it's not already connected then totally forget about it.
But -- good news! I just popped open a 320 and checked, and that pin is not at ground, and it's not floating! In fact, pin 36 on the first SDRAM chip is tied to pin 36 on the second SDRAM chip, and if they bothered to put them together then odds are they also bothered to hook them up to the CPU. I mean, if you go through the work of routing the signal between the two chips, it's for a reason.
So now all we need is a cheap source of the larger SDRAM chips, and some boredom and adventurous soldering.... enough to perfectly desolder 108 pins, then perfectly solder 108 new pins, without a single solder bridge, without damaging any of the traces, and without affecting anything else on the motherboard around those two chips. Where the pins are 0.3mm wide, with 0.5mm of space between them.
Like I said, fancy soldering!
Edited to add: Found the chips at DigiKey
for $6.17 each...