Thanks everyone. If a few more concur, we'll see about making this a sticky. A few more thoughts...
It may be that the only way to eliminate this issue fully is with both improved transmission mounts and improved engine mounts. Transmission mounts can improve feel and precision and do offer improvement in the denial of 2nd issue, but they're not a total fix.If you don't heavily track your car or really push it in autoX this doesn't apply to you. For most, a simple upgrade of the mounts to neoprene provides good bang for the buck and will address most cases of denial of 2nd in normal driving and improve shifter feel/precision.
Rogue Engineering's website says "To eliminate even MORE movement from the transmission, you must go to the root of the issue, the factory motor mounts." Vorshlag says the same thing: the transmission is only part of the problem. This makes sense when you think about it—the engine itself has a large amount of mass and is pretty tall, and in high-G situations it makes sense it would move as well.
There is evidence to suggest that these vendors may have a valid assertion. First, z4mnyc has succeeded in eliminating the issue but only with both engine and transmission mounts (see post). Second, I can point to the experience with my car and Skelekitty's car. The UUC Reds allow me to get into 2nd on an off-camber turn close to home where I pretty routinely cannot get into 2nd in Skelekitty’s Rogue equipped car. However, there is one section of track where for me 2nd is still an issue. So the UUC Reds offer a bit more than the neoprene, and both are better than stock, but neither is a complete solution.
Rogue offers a set of fully isolated hard rubber engine mounts for 380 dollars. (These are similar to the hard rubber BMW Motorsport mounts which cost 800). Rogue notes that there will be some increase in NVH over stock; however, I would imagine they’re much quieter than alternate offerings from Vorshlag and UUC who only offer Red Poly and Nylon.
I'm going to replace the UUC Red Poly with Rogue Engineering neoprene as the NVH decreases my enjoyment of the car. I may move to the Rogue motor mounts at some point as well.
I’d also like to collect more data on the motor mount part of this solution before I update the OP regarding that part of the puzzle. Anyone else have both motor and transmission mounts? If so, experience/impact?