One way that Fox could make Deadpool work is to follow the Marvel formula and put him in a team movie. Originally created by divisive artist Rob Leifeld, the team consisted of Cable, Cannonball, Deadpool, Domino, Feral, Shatterstar, Thunderbird, and Timebomb who took the aggressive strategy that their enemies should be taken care of before they do harm to them. This line-up could work in a movie, but with the only familiar face being Deadpool it seems unlikely that they’d go for a solid adaptation of the original series.
Fox could make an X-Force movie if they took inspiration from the third volume of the comic book series, wherein Wolverine leads a secret task force to handle the missions that the X-Men can’t publicly tackle. Other characters that have appeared on the team in some capacity and been on the big screen are Nightcrawler, Cyclops, Angel, Storm, Psylocke and Colossus. Fighting Mutant terrorists has long been in the wheelhouse of the X-Men in the films so thinking of a reason why this team would need to operate in secret would take some thinking, but maybe it would be best to see a group of the toughest mutants kick some regular human-terrorist ass.