I discussed this with dcamp over email. The issue is that chrome expandos on content objects go on the xray wrapper expando object, which is per-compartment. So with cross-global access (ie, outside the JSM), the inplaceEditor expando is invisible. Patch coming right up.
Created attachment 609508 [details] [diff] [review] Access the inplaceEditor expando with an explicit API. v1 Attaching a patch. Flagging dcamp for review.