(Technical note, I Mac's response, but not Helle's original post?)
I don't have extensive experience calling for visually impaired dancers. I have occasionally had an experienced blind dancer on the floor, but never a sizable percentage. But this is conjecture on my part; please trust your own judgement.
It sounds like you're calling for a bunch of folks who don't regularly dance? In which case, I'd recommend (as with most one-off gigs), not focusing on 'duple improper contras' and just get folks moving to music. Something as simple as a snake dance may be a good kick-off. It's not overly simplifying for them, that's often a dance that gets used at community dances.
It may be worth talking to the sound person ahead of time to see if a clear "head of the hall" can be established sonicly. Some gigs will put up more than one row of speakers or such to blanket the sound, but giving an audio clue about direction may be useful.
If you're shooting for hands-four contras, I wonder if some of the pass through progressions of simple contra dances could be re-worked to have a roll-away instead? For instance,
A1:
long lines
neighbor swing, end facing down the hall
A2
Down four in line, turn as couples, come back
B1
Circle left three places, partner swing
B2
Circle left three places,
balance the ring, gents roll neighbor lady away with a half sashay
As two-swing contras go, that's a relatively simple. Everyone is always holding on to at least one other person. But you've still got changes of direction and knowing your orientation when you end the swing.
But even that is more complicated than I would run for most community dances when most people aren't regular dancers. Even if you have one "seeing" partner in each pair, if you're not separating sets out by "this set has seeing gents role; that set has seeing ladies role" then if you do a neighbor swing, you'll end up with couples that don't have a "seeing" person.
Good luck! And please do let us know how it goes, and what you figure out.