Filipe,
You can do this with JFBConnect, but would need to perform a little extra coding. However, I wouldn't recommend doing this, as it may cause your page to be marked as spammy by your users or automatically detected that way by Facebook. If you page gets marked this way, Facebook can remove it from their site and prevent further use of it. We've only heard of this happening in rare cases, but by auto-posting too frequently, that's a good way to do it.
If you insist on doing it though if you feel it would work on your site and not be spammy, it'd be pretty simple, and we can help you with it. You'd simply need to make sure you're getting the user's publish permission (a setting in the JFBConnect permissions tab) and then with a few lines of code described in the post below, you can add whatever custom text you want either dynamically from the page that's being viewed or hard-coded in:
Posting to a user's Facebook Wall using JFBConnect
Hope that helps get you started, but again, be careful.
Thanks,
Alex