I looked into this in 2007 for a dissociative client who refused to try EMDR therapy. Ulrich wrote this to me:
"I've found that low dose (eg. between 3mg to 5mg bid, depending on body
weight) is a good place to start. If necessary and there's a lot of
dissociation during the day, it's ok to add a third dose in between the
morning and evening dose. There appears to be a non-linear dosage effect
with very high and very low doses working optimally but I do not know as yet
where the cross-over is. The low dose is better for stabilization and long
term attachment issues, whereas the high dose works well for just trauma
processing on a prn basis. However the high dose definitely has side effect
potential (usually nausea and vomiting)."

And then I asked my colleague Bessel van der Kolk, MD (again in '07) who said:
"I have tried it on about 50 patients and have slowly abandoned it, because the reults seemed to be so unpredictable. But I certainly am open to hearing more success stories, and some impression about for whom it works and for who not. Indeed, touch , focusing techniques, breathing and tapping have pretty much taken the place of Naltrexone in my practice."

Anyway, the three other psychiatrists with whom I spoke back then were unimpressed with the results, and one (who had used a higher dose in a client with cutting behavior) said: " I can tell you there was an acute withdrawl reaction from herbendogenous opoids which was difficult for this patient."

I suggest you and/or your T (and psychopharm) speak directly with Ulrich to hear about his latest research in this area.

I don't know what you mean when you say your T has training/experience with DID "but none apparently like me." Have you considered a consult (for you and your T) with an EMDR therapist who's an expert in DID? If I knew where you live I could give you some names.