It would be helpful if you specified what vesrion of Outlook you're using.

In any event you might be able to ALT+A, [enter], J, B.

If you want to create your own hotkey for it look at
http://www.autohotkey.com.  Not hard to do.

Lastly....the blocked senders list in Outlook is so marginally effective
it's probably not worth the effort.  Spammers change their FROM addresses so
often it's practically worthless.

You can create your own ALT+KEY combination by modifying your Toolbar and
add the option to it.
See; http://www.howto-outlook.com/howto/customizetoolbar.htm

I would advise against adding each and every address to Junk since most of
the time the addresses are only used once. Of course there is also no need
to add the address if the email was caught by the Junk Email Filter already.

In general you should be able to manage your junk email with none up to a
handful of addresses in the Blocked Senders List.