Thats really weird because typically the last half of the password is cracked first, not the first half.
If your only using an alphanum table and just the first half is cracked then most likely the second half has a special character(s), alt-xxx, or is non-existent. You will need to create a bigger table with more character space using rtgen or winrtgen. Or you could always take your luck on torrent.
If there is a way to just crack the second DES hash, individually I don't know how. In theory you should be able to, but your best bet is to talk to ChrisG, he prolly knows.