What type of anemones are we talking about here? For example, we know for a fact that gigs and mags ship poorly. Others generally have varying degrees of success.
The big problem with shipping nems is that you don't know what they look like BEFORE they ship it. They could be in bad shape to begin with and then just quickly spiral downwards. Maybe the anemone ate and then they decided to ship it -- I see this happen when fish are sent. Once in the bag, they throw up. Same thing happens with nems. This is where you really have to rely on the vendor to do the right thing.
But, what is the right thing? In an attempt to answer your question, the answer is that there isn't a accepted protocol. On the export end, some exporters ship their nems dry, meaning with minimal water. Not only is it cheaper to ship with little water, but the accepted logic is that because the nem can sense that they are out of water, they don't release any waste.There's no place to release it. The problem with this logic is that it means they hold their waste inside their bodies. No one really knows which scenario is worse -- keeping it in or releasing it into the shipping bag. Other companies -- for example Live Aquaria -- claim to ship anemones with EXTRA water. This increases shipping cost, but the logic for this is dilution of harmful substances in a larger body of water creates a better shipping environment.
To my knowledge, no one has experimented with the different processes. In other words, no one took 5 BTAs for example, and shipped them with various amounts of water to see which arrived in the best condition. Of course, results would be limited because we can't guarantee that the health of each BTA was the same at the onset of the experiment.
Regarding adding chemicals like SeaChem (Prime, Stability, not sure which) or other ammonia neutralizers to the bag water -- I think it may help, but only for a limited amount of time. No one can accurately predict how much ammonia a nem may release in transport. Adding too much chemical could stress out the nem. Shippers have been adding Chloram-X for years and nems still die. It's simply not a guarantee of survival.
Obviously, the best solution is just to get your LFS to order what you're looking for. Once it comes in, you can decide if you want to buy it or not, though this depends on the arrangement you made with the LFS. Maybe you can let us know your general location and I'm sure other reefers can give you pointers on which LFS to visit to order a nem for you.