Well, my first thought was about how little the typical "morale officer" cares. Sorry.
But let's assume you've got a good one!
Are you required to go? Do you like going? Without trying to sound like an ultimatum, I might let the office know that your conscience does not allow you to be defenseless, and you therefore cannot support a meeting that is knowingly being held at an establishment that frequently asks this of its customers.
Remind them that this is the same conscience that drives you to be a member of the military, sworn to uphold and defend the Constitution and its values.
If you can get the morale office on board, this could be a very powerful message to their corporate decision makers.
Regardless of the decision, I would open carry anyway. Imagine how much they should be embarrassed at telling a member of the US military that they can't bring their sidearm into the restaurant. This could make a powerful after-action letter if they did, with plenty of references to the IHOP incident.