First, let me apologise for the length of this post; I think you wil find I've been doing some homework!
Let's assume that you are able to make a perfect hole, one snug enough to the pipe that it can just slip through. What's required there?
I say absolutely nothing- as long as the area of the penetrations does not exceed the % allowed by the ceiling design.
Using that approach, I would say that restoring the original construction, and filling small gaps with a similar thickness of gypsum (ie: joint compound), you've met the design requirements.
Now, joint compound has its' problems- especially whae you start applying large amounts. It drips, it sags, it may shrink or dry. I requires tools, and may require you to have water available.
How about packing the voids with, say, mineral wool? Sure, but then there is the question of whether you've really stopped any drafts. A plumber, testing his patch (made from expanding foam) with a candle ("watch the flame for draft-induces movement) started a fire that almost destroyed the Brown's Ferry Nuclear plant in the '70's.
This accident directly led to the invention, and marketing, of assorted fire stop compounds. In turn, this led to a frenzy of testing, and the listing of the products.
Keep in mind, it was NEVER intended that restoring the original structure be outlawed. These fancy products were simply an attempt to make the job easier! All of the products are tested in comparison to the original structure, and required to be at least as good.
UL publishes several "Fire Resistance Directories." I am sure that there are other references out there as well. Volume 2 addresses the use of firestopping materials.
Many, many systems use mortar as the "fill, void, or cavity sealant." While there is usually a specific product mentioned, the range of products mentioned is so broad as to include virtually every type of mortar there is. (For contrast, the Hilti product is referred to as a "sealant")
Many, many systems use mineral wool as the "packing material."
As for gypsum...5/8 is 5/8 is 5/8...etc. What is important to realise is that if you use joint compound, it is essential that you apply the full thickness. Most of the specially listed materials do not require this full thickness.
Likewise, whether you use gypsum, caulk, or other sealant, you are generally quite limited in the size of the gap you may fill, without having additional support.
The most common form of support used in these designs is filling the cavity with mineral wool. Another method often used is a wire mesh. If you're pouring a mortar, the support is often nothing more than a sheet of cardboard, removed as soon as the stuff has set.
Note in the UL books also stress that it is not a specific product that is evaluated, but an entire construction system. It is quite possible that a material used improperly, or in the wrong ceiling type, will not perform as you'ld expect.
