You can create a SSIS variable that will be used in the connection expression.
Make sure you set the connection to DELAYVALIDATION
You can then call the package from a ASP.net page:
http://pedrocgd.blogspot.com/2008/02/ssis-execute-package-from-aspnet-page.htmlor from a filesystem...
http://biresort.net/wikis/ssis_tips/ssis-dinamically-call-a-ssis-package-filesystem-location.aspxor even other ways...
Regards,
Pedro