On a singlespeed, you can set up that Hussefelt guide so that it never actually touches the chain unless unless the chain is trying to go walkies.
Sounds like he needs guides next to the sprocket anyway, a la Alfine
it's still not deisgned for keeping a chain from jumping due to pedaling with a bad chainline on a flexy bike with long stays, crappy components and single speed. MTB guides are really meant to keep the chainfrom bouncing around when not pedaling and don't really experience much force. i don't think the problem is analagous. I think his problem is when he's pedaling.
same with that above guide, as it is guiding the bottom of the chain, which is slack, onto the cog.
either way it's a pricey fix for crappy mutant bike.