I have seen and used GPG for portable Thunderbird for awhile now via GPG_for_Thunderbird_Portable_1.4.11.paf.exe
Upon the GnuPG site they list GPG 2.0 being available and supporting OpenPGP (enigmail) but only as source code.
So I looked into Gpg4win which is free and open source which aim of Gpg4win is to keep a Windows installation package up-to-date including the crypto software GnuPG.
Therefore I made a new folder in the Thunderbird Portable directory Thunderbird>App>GPG2 and placed some of the files extracted from Gpg4win into this to update and use the latest version of GPG from within Thunderbird Portable.
From within Thunderbird Portable>OpenPGP>Preferences>Basic Settings I made sure the GPG was found in this new folder via the overide option.
The files I used from Gpg4win were
I have tried it a few times and just testing it out now.