Yeah wheat fields can be a pain in the ass even without the hedgerows.
Usually if the enemy can see you you are at least able to see him but if you are already under fire by them it doesn't help much.
However indirect fire uses the ground as a target reference and if that tile happens to be out of LOS you can't get around it easily. Only option would be if a targetable hill would stand behind the wheatfield, so you could use that as some sort of target reference. But in the bocage that would be unlikely.
Mortars/artillery are a bit different in that regard and are maybe the best option here. If you either use an forward observer or a mortar itself you can see that they can often plot a target line behind their direct LOS.
And while a mortar at the front (especially at around 200m) will most likely die quickly or get pinned, a forward observer could do the trick.
And don't unterestimate the power of smoke (either by artillery or grenades) , if you have any. If the enemy can't see you he rarely can shoot at you.
So it is also an option to engulf the enemy position in smoke and storm it.
It would be my least favorite option to be honest because the enemy would still be in good strenght and morale when the knife fight begins but it is an option never the less. Just make sure that you have the superiority in numbers then.