You have to have them dead by C6, right?
C4 is easy as hell. You can take the northeast pretty easily (especially if you class change replacements to Mages, and keep your Archers/Snipers), as well as take out the Thief, leaving only the Cavaliers. Which still aren't too bad. From there it's just lure and kill.
C5 you can kill plenty of units off that come with Hardin. Pretty much everyone but Wolf and Sedgar.
C6 is easy enough without killing units.
Then you have C6x for your EXP needs. Enjoy. It adds to efficiency, both immediate and future.
So in the "perfect run" which is the "efficient run" you're not going to get Wrys attacked by a Hunter.
Efficiently? By turn 3, you can easily get the Pirates to attack Jagen, then have your units feast and/or rape their corpses. Lena hasn't reached your group at this point. And then you can heal people up for the Hunters, who you can easily prevent from attacking Wrys anyway. When Lena comes around, sure she's more useful with Heal, but until then? Wrys has that Heal, and Lena is too far to the north while your shitty units are getting killed.