This is really one of those spots where we could use the courier sprite.
A single cav man that moves from the "parent" commander to the spot you want to check for LOS and when he arrives, provide the LOS exactly as if the Arty unit was there.
Then you can recall the scout to that commander when you're done and, next, send him to the Arty unit you want to move to that spot. When it gets to the Arty, the Arty should perform the move order automatically. Scout could also be used to check for LOS with other unit types not just for Arty.
Totally agree with the market push and I only happened to know of this game from TWC when I read a small post highlighted on the right hand side of the forum. However, I think it's only a matter of time. TWC is a huge community and I'd rather start there than anywhere else because of its visibility profit/cost ratio.