Flt Lt PAS can only be employed in 'flying related jobs', which whilst that definition could be interpreted fairly liberally still restricts them to a flying station.
Ken - not quite. I'm aware of several flt lt PAS mates who are in sh1t 'flying related' ground tours very reluctantly and not on flying stations.
One mate turned down promotion to sqn ldr several years ago specifically to avoid the situation you mention in your second paragraph. However, as Manning told him, he couldn't turn down acting rank and subsequently found himself at HQ Air doing a crap staff job as an acting sqn ldr!