I think a simpler approach than using extra counters would be to give Recon units extended LOS perpendicular to the direction of travel.
If you're moving through limiting terrain with 3 hex visibility, double that laterally so that you can see 6 hexes "left" and "right" and 3 hexes forward from that line. This would change the hexagonal spotting range to more of a rectangle and would simulate a dispersed unit moving along a frontage.
I think that's a good compromise between utility and impact.
Code:
ORIGINAL:
..S S S S S
.S S S S S S
S S S U S S S
.S S S S S S
..S S S S S
PROPOSED:
..S S S S S S S S S S S
.S S S S S S S S S S S S
S S S S S S U S S S S S S
.S S S S S S S S S S S S
..S S S S S S S S S S S