Though you can not connect the mythtv directly as you want to there appears to be another option.
From what I have been reading you can install a MythTV frontend on your Macbook, since it has been compiled for OS X. Then you would have to connect them by ethernet cable to view content on your Macbook. Since I am not familiar with Myth TV I am assuming that when turned on, whatever Linux variant automatically loads your Myth TV backend correct. If not you would need to make sure that it automatically does so and that all of the networking features for Myth TV and Linux start at boot and are available without logging on to the Myth TV, since you would be running it without a monitor.
Your other option would be to make your MythTV's hard drive external and bring that with you. Then connect to it using the MythTV frontend, if that is not possible use something like Video LAN Client to access your video directly.
You may also be able to transfer the files you want over your network beforehand. But if you do this I think you have to delete the file from the Myth TV box, since as I understand fair use laws for recorded broadcasts you can only have one copy at a time.
