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If you google "dual spec 2.4.3" you see a video of a server that has it implemented. So you see it is possible.
They use some ingame npc which makes it even more convenient.

Some TBC servers have features like:
- lower respec cost ramping up
- pay 1000g for 6 months free respec
- no respec cost

Typically, since this is not supported by client, what you could do is...