It's definitely not standard; "creative" would be a euphemism.
The definition of exorbitant is negative, and it has always been so, even in its Late Latin origin (see ODO):
adjective: unreasonably high
Origin: late Middle English (originally describing a legal case that is outside the scope of a law): from late Latin exorbitant- 'going off the track', from exorbitare, from ex- 'out from' + orbita 'course, track'
A modern idiom might be "so far off the radar it's out of sight," which again is more likely to be disapproving than laudatory.
Because of its negative feeling, if you were to use it in the way you describe it's very likely to be considered ironic, where you would be taken to be not particularly grateful at all for your friend's interference.
You could substitute extremely, just use very or (best, I think) leave it out altogether and simply express gratitude with "Thank you for your words of support, which were..." (for example, "very helpful").