This has been added (see the URL-Work relationship list).
The whitelist needs to be disabled still, I’ve added an MBS ticket for that.
The link phrases are kinda unwieldy: “mail-order purchase page for the score of” / “download purchase page for the score of” / “free download page for the score of”. I’d like suggestions for shorter options that still make clear the type and purchase and that it’s a score, if possible.