Generally this isn't an issue / request we see as the upgrade files for SMB appliances are only ~160MB in size.
Mind you this is sort of how the "Manual Upgrade" process already works, you are prompted to proceed with the install(upgrade) phase after the image upload is complete and verified.
I expect if you left the appliance on this page for too long without proceeding however the admin/UI session would timeout in the browser in accordance with the default/configured settings (MAX 999 minutes) and I wouldn't rely on such an approach.
CCSM R77/R80/ELITE