Choosing an account to run a job under - only needs access to the resources it involves?

SQL 2005

I want to setup a new SQL login to assign to a job under, instead of using the SQL agent account.  The job will execute a file-based SSIS package and the package will make connections to 2 different databases, each on different servers.  There are a handful of tables involved.

So, the access needed will be:

- Access to the SSIS package files in a specific folder

- Insert and delete permissions on tables on destination database

- Select permissions on the source database

Can I execute a package using something other than the SQL Agent account?  There doesnt seem to be an option for this, only the Agent account is available.