Nope. Its basically just taking a big risk. Mixing will either go just fine, or they'll get sick and then you treat them, or they die. Really no way around it. I would say that the steps that are most likely to help give you better odds are:
1. Quarantine for 8 weeks to get past shipping/LFS stress, make sure they are eating, and make sure they are used to your water and your routine, and to double check that they aren't carrying something really nasty that is going to present quickly.
2. Keep the water temperature under 74 degrees. I'd even keep it at 68 for a while after the seahorses are introduced to each other. That should keep bacterial reproduction slow, and prevent them from mutating to produce more aggressive proteins. The only problem with that is that H. comes are known for being less active at temperatures that low... so that presents another complication in mixing with them.
3. After the 8 week quarantine period is up, rather than introduce them to each other immediately, start gradually mixing water between the two tanks, a small amount at a time (while keeping the temperature under 74, and preferably at 68-70). That will give them time to be exposed to the bacteria in lower concentrations, and could, possibly, maybe but not necessarily, allow them to build up some resistance.
4. Keep all stress to a minimum. That means perfect water parameters, low to zero nitrates, low stocking density, no temperature fluctuations, no major salinity fluctuations, no pH fluctuations, good oxygenation, good pH, no aggressive or fast swimming tankmates, etc. etc.
However, even with all of these safeguards, you could still end up with a tank full of dead seahorses, or they could live together fine for years, and then the first time you have a temperature spike, or another stressor in the tank, the whole tank (or one species) could fall ill and/or die because they've finally faced large enough numbers of the foreign bacteria that they don't have resistance to.
An additional concern is that with the "TR" and WC seahorses in the LFS, like most likely these H. comes, there is also a risk of parasites, so it would be prudent to deworm them during the quarantine period. I would also consider freshwater dips.