If you're think the KR808D-1 cartomizer what about just the XL
batteries? That's 380mah, quite a few hours of use there and cigarette sized if a bit long. The V4L french pipe is another nice tasting
tobacco with a smooth creamy finish, like butter or custard.
I think you have the right idea, go with cartomizers. If you want to go to the trouble for him you can refill them for him. Have him toss all the empties into a cup/bag/whatever and once a month collect them. Do the boil thing and refill. Since he's either tech-phobic or just doesn't want to bother doubt you'll get him to refill himself.
The eG0 now has a XL 900mah battery vs. the standard 650mah. That's about 30% more life for a couple of bucks more. There's the Hello 016 which is 1300mah but its not an exact match to the eGo. Or the Riva which is an exact match clone at 750mah and cheaper than an eGo setup.
With all of those you're talking a 510 cartomizer.