Mouse 2 (right click) is currently used for absolute menu scrolling (Hold right click or the pen button on the side and you'll scroll directly where you want in the list). The only reason to open osu!direct is to download/redownload a map, but peppy has spoken of future changes to where maps will be fixed automatically. Plus if you need to get to the listing there's that globe button which is the beatmap listing button. As a cheap work around I just open the chat and go to #announce or #userlog and quickly type /np and click the link to get osu!direct to download if I see an update for a map (to make sure I get new files and such).
I don't know maybe there should be a redownload button for supporters to get it from osu!direct. This could be placed in the beatmap options instead.
Reading your post again kind of confuses me (left click opens np links with osu!direct anyways), but I've already written this so I hope this is what you were speaking about.