I don't believe it's possible due to the game engine we use correct?
That's right, company of heroes had a nice ability similar to what's described, you're able to group of select units on screen and without having to deselect them you can pick individual units within the group selected on the control panel.
I don't know it was just a idea. Here's another could you increase the rate of fire on the artillery for ground and water based and possibly ad a saturation and direct fire option like in blitzkrieg the game
There have been some "improvements" to towed artillery since the last public version and some may find they are much more useful now.