How do you link to supporter.php?

I couldn't find this if it has been answered before, it was suggested that I should put a link to the supporter signup area from the add that is in dashboard, or even a page describing the benefits. That some users may not be able to find their way easily enough to the premium button in dashboard.

So my question, how do you link to username.politicallygrounded.com/wp-admin/supporter.php? how would I do a wild card username in front of the rest of the url to the supporter.php?

Thanks,
Brad