WIP Progress: Purple Shiney Card Bag

Well I'm almost done with the card bag, and I've managed to make the "Bag End" (Tolkien reference) rectangular-ish:

As you can see, I've completed the liner as well, and it's also rectangular-ish. Here's where I've hit a major snag. I mean Major Snag. Are you ready?

I cannot do the kitchener stitch. I just don't get it. At all. I mean, I understand what the point is, but not how to get there. Since this bag is rectangular at the bottom, I can't just decrease the liner in the round, nor do the 3-needle bindoff without it being really visible inside the bag. I. Am. Stuck.

I guess I'll have to head to my LYS this weekend and get someone to show me. The real challenge is not to get distracted by all the pretty new yarns there and forget about the whole "kitchener stitch" fiasco.