As far as I understand it, custom Dashboard Plugins can be developed and hosted independently, but I believe our developers in GoodData Professional Services do have experience with that and have developed custom plugins for customers recently.
So if you wanted their help with that, I believe the best next step would be to contact your GoodData representative to discuss the conditions.
Note: I am not 100% sure what exactly are the dashboard plugins capable of doing and what is out of their reach at the moment. So if you would be interested, I suppose the first part of it would be a discussion about the detailed specification.