You could use an intermediate step, like Charity Science’s fundraisers (I’m sure there are plenty of other places that allow you to do this if Christmas/Birthday/Event doesn’t fit your needs) so you can see how much is being donated. Then when you donate the whole lot to Givewell etc. at the end you can ask for a receipt/show it on your bank statement.
You could use an intermediate step, like Charity Science’s fundraisers (I’m sure there are plenty of other places that allow you to do this if Christmas/Birthday/Event doesn’t fit your needs) so you can see how much is being donated. Then when you donate the whole lot to Givewell etc. at the end you can ask for a receipt/show it on your bank statement.