Mohsni was part of a travelling side which won 1-0 at Bristol City on Saturday, and the defender again impressed McCoist.
Talks remain ongoing with the Frenchman and his fellow centre-half Pandza, and the Rangers manager is hopeful both will arrive permanently when the club's transfer embargo is lifted in September.
He 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."
McCoist earlier welcomed Mather's appointment as permanent chief executive.
He said: "I'm delighted about it, absolutely delighted, and I've phoned Craig to congratulate him. I've said all along that we need to get stability at boardroom level and at the higher levels within the club.
"I believe we're getting there now, I really do. I certainly hope so because that's what we've been crying out for.
"The last couple of years have been traumatic to say the least for the football club but things are settling down and that helps."