It is not an easily solvable problem.
As you can see in the thread previously referenced:
http://www.msfn.org/board/Installing-Booting-Es-t118355.htmlin the case of e-sata booting through an express card there is an additional "layer" of complexity (and driver).
The only possible way out at the moment is
maybe to use something similar to the "XP Kansas City Shuffle" (link as well given previously):
http://www.911cd.net/forums//index.php?sho...c=21242&hl=A subsequent thread with a basic batch:
http://www.911cd.net/forums//index.php?sho...c=21939&hl=The method is still VERY experimental (and not fully documented) for XP, and AFAIK noone has tested a similar approach with Vista.
Theoretically, if there aren't additional "checks" implemented in bootmgr (as compared to ones in NTLDR) it
could work, but really cannot say.

If you have a XP license also, you may want to try replicating/adapting the method to the express card+e-sata for XP, and then try to find out if it is portable to Vista.
jaclaz