don't know what you tried but for sure you didn't look where you should.
1 - Add new variable - @package - type string
2 - Add new Execute Package task
2.1 - Select filesystem - create new connection - enter name of an existing package.
3 - go to the properties (e.g. right click - properties which should show up on a window - not a popup window) of the connection created above - you have expressions available - change connection string to be from variable above.
steps 2 to 3 can be executed on a for each loop that populates the variable - or other means if required.