Digital Download Credits On A Pricelist?

Is there a way to sell digital download credits via a pricelist (preferably as a pre-paid)?  I often shoot sports events and sell "3 digital downloads" as a pre-paid item, but then I have to go back and manually add 3 download credits to everyone's account.  Trying to find an automated way to do that.

Create a collection that includes 3 downloads and add that to your pre-order price list.

Does that add download credits to their account?  It looks like after they purchase, there's still something in their cart, but the dollar amount is $0.00.  And it says "0 of 3 Selected".  I guess I'm just not following how that works and whether it's the same thing as when someone just straight up buys download credits.

When a customer pre-orders to come back later to select photos,  that goes into their cart like a collection after they have purchased to select photos for when they become available. They will add the photos they want to download to that collection, check out at $0 and then download their photos. 

There is not a way to pre-sell download credits.

So I would need to put the relevant pictures in that same gallery?  Right now, I don't actually load any photos into the presale galleries.  I just use them to pre-sell.  When the pre-sale is over, I close them.  Then I load download credits to the customer accounts and they use them in a new gallery (for the event) or even other older galleries.  I'd have to rethink my gallery naming convention, but putting the relevant pictures in the presale gallery itself may work.  Only issue is that I may only have one presale gallery (for purchasing) for perhaps both a boys and girls match, but ultimately, those get broken into two new separate galleries once the matches happen. 

You don't have to upload the photos to the same gallery.