The higher their skill, the better they aim, so lower it, that'll give you a break.
Also, you can set a unit's damage to a negative value, that'll make their aim alittle bit wobbley for some reason.
Try 'someEnemy SetDammage -1'.
Last, you could use HD (High Dispersion) weapons/mags.
All JAM weapons/mags come in both a standard and HD version.