This is a question of the type: "Doing X is not allowed. How to do X?"
If a popup blocker allowed you to do a popup, it would be a very bad blocker, and people would not use it.
Please understand that a popup blocker is always a step ahead of you: it uses interface to a concrete Web browser which in turn take a total control of all rendering and scripting on the client side. And your application is supposed to work with all kinds of HTTP client software and be somewhat abstracted from it. From this point, it's easy to understand that it's much easier for a blocker to block your code then break this blocking.