Ok, here's some ideas on how to handle firing though other units.
Firing Through Friendly Units
Firing through friendly unit's position is possible, but unless you've communicated with them properly beforehand, you're going to completely disturb their calm.
If you want to fire through a friendly unit on the same level as you, roll 2D10 (a 'WTF' Roll?). For each die that doesn't come up equal to or less than your unit's leadership, the intervening friendly unit will lose one point of Initiative, and your target unit will gain one point of Evasion.
Firing Through Enemy Units
Enemy units won't be at all surprised that you're shooting through them. So the problem is getting your own men to fire at the unit you want them to, instead of the most obvious target in that direction.
If you want to fire through one enemy unit at another on the same level as you, roll a standard Ld check. If you pass, you can fire at your preferred target (which will be at least concealed). But if you fail, you must fire at the intervening unit instead. If your preferred target is blocked by more than one enemy unit, you must roll a Ld check for each unit you wish to try and ignore, starting with the one closest to you.
(And no, this is not like 4th Edition 40K's target priority rule. That rule required a Ld check any time that you fired at a unit that wasn't the closest target to you.)