Good question. Without setting rules for each army could be hard.

*No special charactors
*No more than one choice from Elites/Fast Attack/ Heavy i.e.
Leman russ one- yes there are different builds you can get but they still fall under the same choice in the book (even by sqaudrons only one tank)
Nobz- cant be troops and can only have one under elites as that is where they are in the book
Space Marines - Captian on Bike, only take bikes as Fast attack as that is where they are. And only one

Still a hard question but looking at new players this could work.