Ok, so I've now got 7DS but alas it doesn't help.
I've since found that Derelict has wormholes, as does Ancient Gift althougth Ancient Gift has so many Wormholes that they are confusing rather than enlightening. Derelict is just the ticket.
So, based off the Derelict map, opened both in Galaxy Forge and Notepad, Wormholes are connected (paired?) by an entry in the .galaxy (map) file in the interStarConnection Section. For Derelict the section is this:
interStarConnection
starIndexA 1
planetIndexA 0
starIndexB 2
planetIndexB 4
spawnProbability 1.0
type "Wormhole"
starIndex[x] n = the star containing a wormhole. The Stars' number refers to its postion in the list of Stars of the map not its name. So Star 1 is the 2nd Listed Star.
planetIndex[x] n = the wormhole to use of the Star above. The Wormhole's number refers to its postion in the list of Planets of the map not its name. So Wormhole 0 is the 1st Planet Entry.
The next Star/Planet entry is the other end of the link and follows the same conventions as stated above.
spawnProbability 1.0 = Always exists
type "Wormhole" = Link type.
The section is preceded by the line interStarConnectionCount -> as always make sure the number of the count is right!
I've gone into this much detail as it appears that Galaxy Forge can neither display nor setup these links. Thus to setup Wormhole links is going to require the map file being edited in a text editor; manually.
I'll test a custom map later today when I get some time and report back; if its as easy as I am making it out to be 
