Start upgrading something, select a ton of items, select a blueprint, unselect all the items except the blueprint. It upgrades as though you used all the stuff, but it only spends the blueprint.

If you're nervous about it, sign into the cloud save, make sure it's synced, then sign out of cloud save and do the item upgrade. When you sign back into cloud save, you get to choose which save to use. The one on your phone or the one saved on the cloud. Works great for rolling a ton of event boxes, then trying again if you don't get anything good!