Sorry about the delayed response. Actually, as you know we can bookmark one link not more than twice in a particular bookmarking website. When the objective is to bookmark 50 pages on a bookmarking site, its not going to be a problem. But when you want to bookmark the same link with different anchor texts, it is a trouble.
What you can do is:
If you have 50 different links to bookmark, use a single account to submit, but make it slow.
If you need to submit single link with 10 different target keywords or anchor texts, create different accounts. But be sure, when I tried doing this, it showed me an error saying "the domain already exists"