First off, by way of the FAQ, you are not going to maintain that pressure. The TB and IAC are "capping" the system which they will NOT due...especially the higher psi you go. So your boost reading only 5 is probably accurate.
The Kenewagner does it (I do it the same way) is to cap off your PCV valve and your crossover breather (intake tube to driver's valve cover). This way, you don't end up pressurizing your crank case. You don't want to do that because it will artifically show you that you have a leak.
Then you want to pressurize the system from the intake tube where the MAF would attach to. By doing this, you WILL pressurize the entire system...(air gets right by the TB through this, but you could turn the key on to open the IAC as well) Then I do it every 5 lbs...spray each joint with soapy water. This will blow bubbles if there's a leak...very easy to see.
Make any adjustments as you go...work everyplace (to include vacuum lines) to ensure that there are no leaks. Then when you're done, go up another 5 lbs and check again. Repeating this process will eliminate any leaks that you never knew that you had. Some vacuum lines are under boost when the car is, so it is also good to check them. And it works great to find any other leaks that may be occuring along any of the other vacuum lines as well.
It'd help to have Ken's nice little tester. If you like, you can check with him to find out how to get one if you'd like.