https://www.backcountry.com/explore/how-to-make-a-shot-ski
Or I mean if you dont wanna put that much effort into it you could just buy some contact cement or gorilla glue and just glue some shot glasses on it, or buy adhesive velcro and velcro the shot glasses. But in my opinion just get a forstner drill bit, put shot glasses on your ski, outline with sharpie then drill a deep enough hole for each glass. Pretty much what that article says.
Also you may not want to do it if the skis have any metal in the core, probably a solid wood core would work best.