Simply no.
Offensives can only be started from a frontline. Which can only be 'drawn' at a border.
Inland you can have a defensive line, but you can't have both at the same time for an Army. (They will replace eachother)
As to why they do it like this, fairness. A player should have always the chance to see what is coming for him.
(There was a post by podcat somewhere about this. I will try to find it.

)
Edit:
Vidkjaer said: ↑
Is it possible to make a fake frontline in your own territory?
For example I don't want to position my troops at the border and give away Intel on my panzers, but instead make a fake frontline one province line back and advance from there?
Granted the time moving one privince Will take its toll on the bonus, but coming as a surprise could prove beneficial.
a front line needs to be drawn only on the border of an enemy, so if you hold back troops as to hide them you cant get them the bonus. they need to be in position for it to start ticking up (and a good thing it is so you can get some heads up that a front is heating up)