I can't recall when Connect would allow selective syncing.
The only way I can see you getting what you want is to connect your watch to a PC via USB and manually import the activities from web Connect's activities page and the Garmin/activity folder on the watch. Just make sure Bluetooth is turned off as activities often sync automatically.
I guess steps, sleep, intensity, etc. aren't important to you.
What pshare suggests is a good solution. Another one is creating a common GC account for the device, and then separate accounts for each of the users. You'd associate the device only with the common account, syncing all activities only to it. You can then export individual Activities in the "Original" format and import them to the respective personal account (or even downloading the FIT files directly from the watch and importing them).