Presumably you could split aiming into reaction, dexterity, and precision. (You'd probably want ranged based accuracy built into this mod)
Reaction would still govern your ability to perform a reaction shot, but now also governs shot accuracy at very close range and with pistols when using snap or auto shots at medium or long range.
Dexterity would govern your ability with rifles and heavy weapons using snap and auto shots at medium or long range, similar to firing accuracy.
Precision would govern your accuracy with aimed shots.
Both dexterity and precision could impact your throwing accuracy.
The idea being rather simple: Until you start getting to the distance where aimed shots are necessary to have a reasonable amount of accuracy, it's not about making precision aiming adjustments, but about dexterity and grace at medium range, or about reaction time at short range. You could mod in some range penalties to pistol and bump down their TU times a bit further and make them very attractive short-medium range weapons for clearing crafts or fighting in buildings.
Likewise you could play with accuracy to make rifles excellent aiming weapons, and heavy weapons more medium-range autoshot kind of pieces, enforcing some specialisation.