The Issue: To show the origin callers ID on the mobile, not the forwarded number (Our telco has fixed their side

I´m trying to calls that are made by "External Forwarding" to a different trunkgroup with different NPD. But the fwd doesn't work, if I change "NPD for external forward" from -1 to for example 10 that works, but I dont want the whole PBX do that, just only when a specific TG is accessed. (Via Discr/ARS and so on).
My TG´s NPD selector for public calls have the value of 10, so it should be used for ext fwd, but nope, it doesn't work.
(Note. We use ARS pro tg size + discr selection)
From the doc:
NPD for external forward
-1 (default value) = external forwarding in compliance with the NUMBERING PLAN DESCRIPTION No of the trunk group. (<<< Does this mean that ext fwd use the Trunk Groups/Trunk Group NPD selector)
0 to n = NUMBERING PLAN DESCRIPTION No to be assigned to the external forwarding of sets. It has priority with respect to that of the trunk group.
NUMBERING PLAN DESCRIPTION (see TRANSLATOR) allows received numbers to be translated (Incoming calls) and called numbers to be built (Outgoing calls).
I´ve probably have misunderstood the text.
Any ideas.
/S