When I wanted to use my iPhone micro-SIM in a Galaxy Nexus, I needed to make it fit. I didn’t want to wait around for a mail order adapter, so I found an old SIM and cut a hole in it with an X-Acto knife. I put the micro-SIM in the hole and secured it with a piece of Scotch tape:
This went easily into the Galaxy Nexus. Getting the back cover back onto the Galaxy Nexus is somewhat fiddly, but I discovered that the hooks engage most easily if you engage the very end of the cover first, then bend the back fiercely to engage the hooks.
Once those main hooks are in place, the cover is aligned properly and the other retaining clips pop into place with moderate pressure from the thumbs.