A.H.
We just had a similar problem ourselves. Where are all the practicing Catholics these days, right? We asked my sister to be the godmother for both of our kids. My husband's family is not Catholic, either. So, my sister is the godparent for both, and my brother-in-laws are Christian witnesses, one for each of the kids.
I also believed that our kids needed good role models of faith that were going to be involved in their lives, so we decided right away that it would have to be family (as close as some friends are, you never know what will happen with them down the road). And, of course, one has to be a practicing Catholic. I have two sisters, but only one is still Catholic. So, even though I didn't want to burden the one sister and offend the other, we still went ahead and chose the same sister twice.
I don't have any suggestions for asking creatively. We just called them up and said, "Would you like to be (insert child's name here)'s godfather/godmother?" after the baby was born. When I asked my sister the second time, I said, "How would you like to be a godmother again?" She was super excited both times. We agreed that it's not about gifts, but about spending time with the kids and giving them an example to live by.
Good luck with the birth and the godparent choosing!