Anyway I have tried it, one needs 26 levels of Druid for 8x Wildshape, which unlocks Dragon Shape, which unlocks Dragon Companion (not to forget to mention one needs Epic Animal Companion feat as well). If you take a 3 level dip, and with the 3b20 Rule, that level 26 Druid comes on Level 29 of the Build...and the last available Feat slot, thus, no additional slot for Dragon Companion.
I was looking for a Druid 27 / X 3 split to add some flavor to my Character idea, but I just can't get double-dragon-trouble if I want to dip.
MAKE DIPPING GREAT AGAIN!!!