Mohsni, who has been training with the Scottish outfit in recent weeks, is currently without a club after leaving Southend United at the end of last season.
Meanwhile, Prandza, who has been linked with a number of European clubs, departed Mechelen earlier this month.
McCoist told Sky Sports News: "It would be brilliant if we could get the two of them - a Christmas cake scenario.
"Boris is a really good standard of player, and our chief executive Craig Mather has been in talks with his representative. I'd be absolutely thrilled if we could get both.
"Bilel has been terrific for us, and we'd obviously be keen to take it further and offer him a contract. I think he's happy at the club, he's settled in well, and we've certainly liked what we've seen so hopefully we can get the deal done. I'm hoping it's just a matter of getting the paperwork done."
Rangers will play in the Scottish second division next season.