I checked my first bagged cuttings for the first time yesterday, and low and behold, I already have rooting. They have been bagged for 13 days. Since it took so long to hear back from anyone on how to go about this bagging experiment, I did it differently. I used 100% moist, long-fibered sphagnum moss as my medium. These plants were cut on 6-20 and were bagged on 6-26. Leaving more medium-size leaves on these plants than I normally would did not seem to hinder their rooting. The cuttings in my typical 100% perlite have done absolutely nothing, and some were cut a month ago. Notice that I simply tied plastic-coated wire around the bag and moss, so this does allow some water vapor to escape. Subsequent bagging was done, still with moss, but I used painter's tape to seal the bag rather than the wire.
Of interest is what sunburn looks like. I made the mistake and left my cuttings out in the midday sun (for a single day) after they were first bagged. I knew better. Not having a leaf-canopy to protect their stems, cuttings will be very prone to sunburn. In fact, in my experience, mostly leafless cuttings (or potted plants) are about the only sort of plumeria that will sunburn. Generally, those rooted (and potted) plants will have that nice leaf-canopy, shading the stems from the harsh sun.

Sunburned plumeria