Actually, since your running omna's, why don't you just run the tren till week 12, maybe with some prop.
AAA (nice name) of course you can run tren and d-bol at the same time, I bet it would make a very nice short cycle. The reason I reccomend he use it at the end vesus the front is that he's got the d-bol at the front to kick things up a notch, and at the end he'll have the tren to do the same. It will keep his weekly total more stable, instead of it being high at the front then low at the end. Like if you were running the omnas for ten weeks and someone asked "should I add 800mg deca for 5 weeks or 400mg for 10 weeks?" Obvoiusly the later.