Get an additional barrel from ILWT or find a factory take-off IMO and then pin/weld a shroud to it.
I have two MPX SBR's and usually plan ahead on forms, but on short notice out of state, if you put a 16" bbl in it, it's no-longer in SBR form and no longer requires the ATF's blessing to travel with. Shoot it in 8" config at home, slap the 16" bbl in it if you need to. the shroud really doesn't add much weight and I run the same HG, so it's not much different other than movement/spacing from walls.
If that's too much coin, just SBR it for $200, file an E-form 1 and be done.