In this Scalpel model, which is a few years old, it is possible to fit 27.5-inch wheels, but the bridge connecting the lower chainstays must be modified.
As shown in the photo, you can see that the original thermoplastic bridge has been removed and replaced with a new carbon one, which allows for better front wheel clearance.
Gallery
Modifica Cannondale Scalpel
Passaggio ruota foderi inferiori modificato su Cannondale Scalpel