Anyone know how to get a gold rank on 4-5? How do I pull it off?

It's not too hard once you figure it out.

WARNING! SPOILERS AHEAD!

1. Remove the blocks. Cover the gap between the platforms on the right.
2. Start the first mini on the right. He'll step on the switch, then wake the minis on the left.
3. Before the left minis get a chance to move, reconfigure the blocks on the left into stairs that to point to the right.
4. The minis will climb the ladder and smoosh the button.
5. As your first mini reaches the same column as your sleeping mini, activate the last sleeping mini.
6. Reconfigure the blocks on the left in stairs that point left.
7. The mini at the bottom will climb the stairs while the other minis will take the ladder, get the card, and catch up.

Wow, I actually probably would have never figured that out. Thanks. Do you also know how to complete 4-6? I can't get the minis to the door.

4-5 took me a few tries to get right, as I recall -- good level, requires a bit more coordination and timing than most. I did it a bit differently from the solution above, but a similar strategy.

Just reverse the direction of the minis by building a wall next to the top of the pipe, then make sure the blocks are cleared so they can successfully sproing across.

I'm all the way on the plus levels now. It gets pretty crazy on those levels.