I'm not sure what you're asking, exactly. I think you might be under the impression that the rules are stricter than they actually are. You can donate whatever you want to the Charity Corner (provided it fits the theme, but the last couple of Charity Corners didn't really have many restrictions). When donating something, it'll be taken from your inventory, but where you store the items before that is irrelevant. You're also free to buy new things to donate even while the event is going on; the only stores that will be closed during the event are the Ever-Stocked General Store and the Neohome Superstore. But you can buy whatever else you want, and keep it in your SDB, your gallery, your inventory... wherever. It might be useful to check out the link I posted above, which describes last year's rules, and JellyNeo also has a list of a few donation strategies which might give you some insight into how the event works.