KennyTM has crafted a Mobile Substrate extension which fakes push notifications. Being that jailbroken apps can run in the background they don't need to use Apple's push notification services. However, in certain cases it would be nice to have notifications delivered in the same way Apple delivers theirs.
The MobileSubstrate extension called FakePushNotification can be installed in /Library/MobileSubstrate/DynamicLibraries and then be utilized by applications like so:
FakePushNotification com.yourcompany.pushEnabledApp -
body = "Hello world!";
action-loc-key = "Welcome!";
You can download FakePushNotifications from here to try it out. This is not a final release and may contain bugs.
[Example of push in official app]