You could just message a moderator in game on that day, I'm pretty sure that there will be one online Good luck~
true true.. but some days are so chaotic in chat I'd rather take it to forums. Thanks for the help though
The easiest would be for you both to confirm (on forum, in this post) exactly what you are trading. You can leave the items in a locked chest on your island for us to pick up and process the exchange. You don't even need to both be online.
A mod can take the items then you can both be online for the upgrade. Then when the upgrade is confirmed done you message the mod and they will give the items to the person who needs it
I might not be in game for a while but if you leave them in a Locked chest labeled near your spawn I can take them
The person being upgraded should be online, because depending on the upgrade there are some one-time items (e.g. enchant table and spawner for donor50) that can glitch and fail to reach you if you are not online. If you do not care about those items then it's not necessary to be online when the upgrade happens.