If you have a 28-pin ZIF, you can check out the 28-pin position of a PIC in the 40-pin ZIF and then just delete the connections you won't use.
You can download the Winpic800 software and install it. Then from the PIC list, you can see how different pics are supposed to be inserted into the ZIF socket.
For example, a 28 pin PIC18F2450 has to be inserted from the first pin of the ZIF socket.