Just managed to unlock this solo using 2 controllers. I am unable to post a video of my run through as I don't know how, but if anyone wants more info on how I did it please message me over live.
Start off the level (Woodland Vestibule 1-1) with 1 character's item as the magnet and the other character's as the repulsor. There aren't to many difficult parts in this level and alot will be trial and error. I found it easier to always position the character with the magnet equipped in the elevated positions, jump with this character and then press
to attract the chariot towards you, now with the second character use the repulsor while the chariot is still in the air to repel it to the elevated platform (unless you are able to place the repulsor character directly underneath). Where possible stand directly underneath the chariot and use the repulsor to send it directly up in the air. Then use the magnet to pull it towards you, this way is much easier as the chariot takes a controlled path as opposed to a random one.
Sorry its very vague but I hope this helps, as a side note the items I used were not upgraded at all, so it may be possible to do this solo with an upgraded magnet. (I will be checking this theory once I have found all upgrades).