After guest checkout, user cannot create an account with that same email address (digital goods)

This is probably a rare case, but I want to post my solution to this:

If your shop sells digital goods (commerce license), you need to keep the "Create Account..." rule active for guest checkouts. Otherwise the customer cannot download his product.

This rule originally creates an account with the order e-mail address both as name and email. If the customer later returns and decides to create an account, he will get the error message "This email is already registered". It is not possible to do the password recovery and change it to a regular account. He needs to create a new account and use a different email address.

To avoid this, I altered two checkout rules. They now assign the order to the user account via order-id instead of the order-email.

#1
In the “Create a new account for an anonymous order (HTML)" instead of the order-email address I use the order-id as user name and a dummy email address as email ([commerce-order:order-id]@myshop.xy).
#2
In the "Assign an anonymous order to a pre-existing user" the dataselector now uses the order-id instead of the order-email (both in the condition and the action.

Maybe this is a bit of a work-around but so far it works. Any ideas for improvement are welcome.