Based on what you've presented, I'd simply file the motion to terminate with the IJ and let him/her make the decision. Getting DHS to agree (while they should and probably would) may take more time than filing, letting the response time elapse and then the IJ issuing the decision.
You should have your attorney file a motion for conditional termination of proceedings and speak directly with ICE counsel about it. The Immigration Judge is unlikely to terminate without ICE's consent. Based on the facts as stated, you stand a good chance of having your matter terminated. One question though: why do you think that it is better to have your adjustment application adjudicated by USCIS rather than the Immigration Judge?
The immigration Judge cannot terminate your case in this scenario without the consent of DHS. In Boston, while you can administratively close the case, maybe, it doesn't seem a termination is likely. Sometimes, adjusting in front of the Judge is quicker and more efficient than in front of USCIS so termination may not be in your best interest. Speak to an attorney about your case or make sure you are talking to YOUR attorney in order to understand what is going on in your case. Good Luck.
Massachusetts Immigration Attorney
508 455 4241