must externals be defined at startup?

[RGould8 at aol.com]

I'm reading the docs for the "externals" command:

Specifies a list of files containing external code that are to be loaded into 
memory when the stack opens.


I've got a Revolution app that resides on the user's hard-drive, and then 
calls anothe Revolution app off a server on the internet.   Can I define 
externals when the hosted Revolution app loads, or does it all have to take place 
beforehand by the locally-run app?

For instance, could I store by externals on the host, and have the 
host-stored rev app load those externals?