To use Bluechart maps with Garmin Mobile PC, you would need another key to unlock them to the 20x. Transferring them is just a matter of using the Map Tool in MapSource to select the areas you want, then the Send to Device to transfer them to Mobile PC. If you have not done this before, Mobile PC must be running the first time you attempt a transfer. Further transfers do not require Mobile PC to be running.
However, BlueChart maps do not work fully with Mobile PC. Many of the symbols and features will not display. For the computer, nRoute is a better choice.
Terry