What we do is fake a line appearance with phantom extensions in a hunt group. Have the inbound sip call ring the hunt group, which in turn will spread the calls to the phantom members. On each person's phone, create a secondary extension key for each phantom.
The downside to this is that they have to push the key to answer the call, no auto-answer, and when they do answer it will move the call off of the phantom and onto their personal call keys. To then put it back on hold for anyone to answer we have them "park" it by doing a transfer to hold of one of the phantom keys.