You seem to have a good handle on what's going on. But for the benefit of others, I'm going to offer more background on what's going on. (You will pick up whatever you can ...)
Well, I'm going to be the bearer of more bad news. What's happening up there is the roof is getting heated (especially in the Summer) and the heat is radiating into your living space right THROUGH the sheathing, insulation, AND drywall. This is really bad especially in summer where your A/C is running all the time. You'll probably NEVER cool that room. And in Winter, you have the same effect except less so but you will have moisture up there as it cools.
Before there's any recommendation to the 'problem', let me explain what should have been done when the attic was finished off. Whoever finished off the attic should have installed Soffit Vents and Soffit Chutes and a Ridge Vent. The Soffit Vents are installed at the eaves which allow fresh air to rise up and along the UNDERSIDE of the roof's sheathing via the Soffit Chutes (to cool the roof), and to channel the hot air to the outside via the Ridge Vent. When this doesn't occur (as in your case), adding more insulation isn't going to help. In short, the roof needs to be kept 'cool' in order to prevent any heat from building up.
If you want to know what a Hip Roof is, see Shingling a Hip Roof (assuming this WEB page loads up.)
For more info, see OwensCorning.com and there are pictures and product links too. (They call their 'chutes' - Rafter Vents ...)
Now what should you do??? That's a good question! If you need a new roof, consider installing the lightest colored shingles you (... well, your wife) can tolerate. This will help a little to keep the heat off of the roof. Beyond that, I'd consider installing the Chutes even if you have to cut out parts of the ceiling. BUT, before you do, I'd learn as MUCH as possible about what needs to be done to have a successful 'retrofit'. (Get the proper sized and type vents and chutes. Yes, they even make Soffit Vents if you don't have eaves on your home!) If you need more info or guidance, post back.
My best to ya and hope this helps.
Jay J -Moderator
PS: Hopefully I've made it known, indirectly, that you don't want to use PVC as a 'chute' ...
PPS: You can always take your chances ...
PPPS: God Bless America!