To even unlock these you HAVE to collect all the safkas, which are the little creature guys you collect and follow you around, in every level. I found a some videos that is a complete walkthrough of the entire DLC. Although it has commentary, which some may find annoying, but I thought it was rather enjoyable. Either way, he runs you through every level including how to collect every safka. All the credit of these videos goes to the youtube username of thelisoncruz. All I did was find these ;) Also if you only need to beat the bonus levels, having them unlocked already. Watch the 4th video for the first 3 bonus levels. He hasn't made an 8th video for the last of the bonus levels yet. I will update when it becomes available. Reason he doesn't have the last video is due to the fact that the level is still glitched. Still these videos can help you get most everything done till the new video is made and an update fixing the glitch. I hope this helps you guys out. Thanks for reading all this ;)
EDIT: The 8th video is up now for the last 3 bonus levels.