Umm, hate to say it's been done before (though I already have) but it has. Star Wars Galaxies had player ships where you could invite others to man ship turrets and use repair kits to affect repairs. It was fun, but admittedly the most fun was had by those in the cockpit and turrets. Unless you have tangible rewards for doing these noone's going to want to do them, which is why it never really caught on in Galaxies.