I think both Soundwave and andreeje have good ideas here.
Re: Soundwave’s suggestion - Perhaps you could carve the sigil in wood, and if your friend learns tactile imaging, they could trace it a few times physically, and then continue tracing it with tactile imaging until it “opens”. You could possibly also trace the sigil on their hand or other body surface a number of times and then they could keep tracing with tactile imaging.
Re: andreeje’s suggestion - Yea, you could potentially involve this person in your evocation work, perhaps even tasking on of the entities you evoke together to help open this person’s sight. Obviously visual sigil opening is not necessary to evocation, it is just a good tool for those of us with sight. I’m sure there are other methods, including opening them with others for a while.