Don't know about current officers sitting there but they didn't take bribe when I went there few times.
Just print out the AliExpress order page mentioning its original price.
Go to GPO lahore, get a form filled by people sitting at entrance (entrance from mall road). Make sure to bring that letter and printout with you.
Then take that form to IMO at the backside of GPO. Get it signed and bring it to Inspector's office along with the file given by IMO people. (inspector's office is located in front of bikes parking) They will assess the value, cause you some headache and put custom on your items.
Postman will bring your items and you will have to pay custom duty to him.