I don't think there's a specific tool for that, why not just manually pose the ragdoll to be sitting?
i do this all the time
if a ragdoll has really limited rigging i have the ragdoll mover for that
so in my opinion, just get used to the idea of using the physgun, i've done all my posing mainly with the physgun
it also gives you a chance to give each ragdoll a different character
i mean how boring would a scene look if everyone stood the exact same way