I don't know the answer to your question, but wouldn't an easier option be to install the largest capacity, highest class, micro SD Card (that you can afford), permanently in the card reader slot and use that as your data storage drive, leaving the eMMC storage as the OS and program drive?
I think that the price per GB between an SD Card and a SSD are nearly comparable. I may be wrong on that though.
This option has the following benefits.
1. As the card reader is not located on the docking station you can use the Transformer without the docking station and still have the storage.
2. It would allow you to safeguard your data (if you forget to do a backup) in the event of a failure of the Transformer Book (I know having an SSD installed does this as well).
3. It is able to be easily removed either for safekeeping or for use in another PC.
4. The card is unobtrusive and not in the way.
The downside is if you wish to use the card reader slot for other purposes.