Currently, the transpose button must be held, for each transpose to take place. This is already documented as highly inefficient and is being looked at for a future update, to be remedied.
Currently, the KSP cannot be transposed via Midi. I know the BSP can and I would like the KSP, to behave the same. I have already brought this to the attention of the developers and it is noted on the backlog, hopefully, for a future implementation.
If you feel strongly about wanting this, I suggest you contact support as well and let them know. The more interest that is shown on a particular subject, the greater the chances are, of it being implemented.