That poor dog has already lost his master, can he at least keep his dignity? A console command would be preferred over having to use a mod.
I realize you said "no mods" but what about making one yourself?
You could use the GECK: http://fallout.bethsoft.com/eng/downloads/geck.php
There is a way to edit attributes of NPCs: http://geck.bethsoft.com/index.php/Category:NPC
Then you would save your mod as an ESP and it wouldn't break achievements.
Here is how you do it with the console:
Open it up, click on Dog Meat to make sure he's selected, then type in:
Note, opening the console will prevent you from earning any achievements for that session. You'll have to save the game and then exit the game and go back in to continue to earn achievements.