1. Sit down and try to squeeze it out. It may take half a hour, but you'll eventually get to a stopping point (totally giving up / finally pissing).
2. If unsuccessful, get up and stand for 5 - 10 seconds.
3. Sit back down and give it a minute, don't force it. Some reflex will kick in and the flow will start. Repeat this step a few times if necessary.
It's worked for me the past the few times I've run into this problem. I can't guarantee that it'll work, but it's worth a shot.
2. If unsuccessful, get up and stand for 5 - 10 seconds.
3. Sit back down and give it a minute, don't force it. Some reflex will kick in and the flow will start. Repeat this step a few times if necessary.
It's worked for me the past the few times I've run into this problem. I can't guarantee that it'll work, but it's worth a shot.