I also have a rat sputnik and a rat tunnel tied to the roof
You can tie any kind of tunnel to the roof or sides of a cage with sisal string, but it helps if they lead somewhere - ie from a house roof to a shelf or a shelf to a sputnik eg.
Also Erin's Hamsters has a good hammock made from toilet rolls! You'll need some sisal string really for hanging things - it's safe for hammies to chew unlike normal cotton string - not always easy to get hold of though. Online craft shops sell some I think. Where did you get yours from Coco? I got some that came with another toy.
https://www.youtube.com/watch?v=NuPeyD6w-CI
Our hamster likes any kind of tunnel or hidey place at floor level - and they tend to like lots of deep substrate too (you don't have to use up too much by having it deep as you can just spot clean mainly and the bottom layer stays dry).
Otherwise he's not interested in toys and things unless they have food stuck on them! They do seem to like ceramic mugs or pots. I have a salt pig that our hammy likes to sit in and eat his monkey nuts. It was supposed to be a sand bath but he decided it wasn't going to be a sand bath.