Looking at it further, it seems to be even more tedious to deal with because when the URI index.php/admin is decoded, a login form is rendered and when it is submitted you need to go back through index.php with the same URI of index.php/admin plus the login account and password stashed in $_POST. If you forget to update $_SERVER['REQUEST_URI'] back to index.php/admin at the breakpoint at the top of index.php again, you don't get the correct decoding that provides the route through userid/password verification, and you end up being shown the login form again.
 	
	| http://example.com/magento/(index.php)/customer/account/index/
 ^        ^           ^        ^     ^
 |        |           |        |     |
 |        |           |        |     ‘- Action
 |        |           |        |     (indexAction())
 |        |           |        |
 |        |           |        ‘- Controller
 |        |           |        (AccountController)
 |        |           |
 |        |           ‘- Module (frontName)
 |        |
 |        |
 |        ‘- Optional
 |
 ‘-- URL prefix
 
 | 
I can't think of an easy way to handle this using the launch facilities PhpEd currently provides. If anyone else has figured out a way I would be very grateful to hear it.
TIA,
Nick