I would like to recommend a product
We noticed that pets at home has started stocking these rosewood naturals boredom breaker treats. There is a huge variety of things and they are mainly aimed at rats, rabbits, chinchillas and degus (and our rats give them a big thumbs up)...but there is a lot of stuff that is suitable for hamsters as well and they don't stuff them full of things like honey & colourings so they are healthier than most bought treats.
They do normal stuff like sticks but also 'pizzas' and mixes and...dum da da daah...a log filled with millet and dried carrot. We got our robos one and they lurve it
They tend to come out as soon as they suspect we are giving them food and when I put this in they shot out and started climbing all over it and stuffing their little faces. It's going to last them ages but once they've finished it is a handy cage accessory as well as the log is hollow with a hole at each end and one on the long side and just the right side for tiny little robos. It'd be a bit small for the larger hammies but I'm sure they'd still enjoy eating it and the many other treats in the range.