system-files does not provide execute access - so this is not possible. The only way to have a snap execute binaries already present on the host system is via classic confinement - however a snap must be granted an exception to use this via following the Process for reviewing classic confinement snaps - also note the there a number of downsides to using classic confinement as well:
- classic snaps can be brittle since they run in the global mount namespace as opposed to the strict/devmode runtime environment whose rootfs is a base snap. While the snap is built with a base in mind, its binaries or environment variables are adjusted to point into the snap where the host’s filesystem is fully available, which can lead to problems cross-distro, running host commands with the environment variables set, etc
- classic confinement is not available to Ubuntu Core and therefore the snap would be unavailable to all-snaps devices