Vacuum Pump / Brake Booster Pump O-ring replacement

[rebouch1]

My first post to this forum. Thanks to all for the good information on this forum!.
I've been fixing a couple of oil leaks on my 2005 4.8is...one I found to be the lower oil pan gasket and the other is the vacuum booster pump O-ring. My question is: Does anyone has a good trick to put the vacuum pump back into the engine? The problem is the little flapper/driver that connects to the engine tends to "flap" into a position that will not allow me to seat the vacuum pump fully into the engine cavity. I've actually cranked the engine a couple of times to try align the groove that mates with the pump vertically to see if I can get the vacuum pump in without it flapping out of position. I have not been successful in getting the notch to be completely vertical, which I suspect would help. I have frustratingly tried to get it in for about 3 hours...no luck. Does anyone have a trick to get it in?

Thanks for any info you may have. - Rick-