Here's a couple ideas..
Special Pilot Ability: Anti-Aircraft Gunner
"Just like shootin' clay pigeons..."
Prerequisites: Sensor Operations 4+; BM/Vehicle with Anti-Aircraft Targeting Design Quirk
XP Cost: 100
While most tactical Air Defense units maintain a very small threat bubble so as to be able to turn their guns equally well on ground targets, their powerful search radars can be exploited for maximum effectiveness against air targets at the cost of not being able to acquire firing solutions on ground targets.
A character with the Anti-Aircraft Gunner may spend one round recalibrating and up-powering his sensors to enter 'Anti-Aircraft mode'. After that round has passed, his BM/Vehicle is treated as having presence on a low altitude map, and may engage targets at that scale as if he were piloting an Aerospace fighter. Similarly, the un-dampened sensor emissions provide an easy beacon to any airborne sensors, and the BM/Vehicle may in turn be engaged as if it were a target at altitude 0 and Velocity 0.
While in 'anti-aircraft mode' the BM/Vehicle may not engage targets on the ground map, nor may it stand in trees or similar terrain due to massive sensor interference. The character may exit 'anti-aircraft mode' by expending another turn to do so, returning to normal targeting rules afterwards.
2nd idea:
Careful Aim House Rule: In addition to everything mentioned on pg 84 of TacOps, each round (two rounds, in ATOW) of careful aim DOUBLES the maximum reach of Extreme Range. For example, after 1 round of careful aim a Medium Laser may engage a target at 24 hexes. After 2 rounds, 48 hexes. After the maximum 3 rounds, 96 hexes.
My thoughts on the house rule: For my own games, I'd also REMOVE all references to damage penalties. (since ranges much bigger than that in ASF dogfights don't suffer any..) But other than that, I think it's a fairly simple rule that is more or less in line with the existing Careful Aim and Extreme Range rules. I'm fine with NOT requiring a SPA to make use of it, since the loooong time between shots is plenty of penalty right there. If a target can't/won't break LOS in that amount of time before death comes from kilometers away, it deserves to be shot. And it pretty much satisfies my desire to see 'better vs real world' comparison.. while real world tanks may be hitting from 4,000 meters or more, they're not doing it 6 times per minute.