There should be checkbox near I m ready, juggler, otherwise I dont buy it. Also by ticking juggler it sends silent private message to current host !juggleme or !dontjuggleme, on join it would send only !juggleme otherwise be silent so host would know lobby supports juggler or not.
And actually I m trying to implement this, but I m not good at programing at all, I made new list near ignonePm which users can juggle you, but I guess Licho idea is better(no messing with allow juggler list) but dunno about lobby admin, because we know licho habits to troll and send everyone to PW or something, but he can !troll using springie too then only juggler checkbox might be handy.