Bully has a furry guinea pig, which he beats up on a daily basis, then apologises to it at night time and cuddles up to it! I have tried him with various other 'real' boy guinea pigs of different ages to no avail so this is the best option which he is very happy with!
Also when he and the others come out of their cages, (seperately), I have loads of different toys, i.e.,wooden logs, balls, kitchen rolls,fluffy toys etc, and beds, tunnels etc under my bed where they play for ages, Bully is the most interested in the toys though, the rest seem to like the hidey holes and beds!