It's the only solution. The flipside to your corporate evasion strategy is that corporate reporting tools need to know what is running on their systems, especially if it's malicious. You might have bought the license to the program, but they own the machine you're running it on, which makes them just as important a stakeholder as you. If they don't want you running that program on their machine, they should be allowed to know about it, for equally obvious reasons.
The issue with allowing renaming mIRC is that it makes it really easy for trojans/malware to repackage mIRC and sneak it onto someone's system. Believe it or not, this was and sometimes still is happening. The same double edged sword that you want to use to evade your corporate policies is what malicious virus writers want to use to evade detection on normal users' systems.
The other and more pertinent issue with forcing the mirc* prefix was that scripts used to repackage mIRC as myscript.exe, passing off the exe as their own original work. Not only is that an insult to the actual author of the program, it also violates the EULA which strictly prohibits the redistribution of the executable without permission. Disallowing this name change successfully cut down on script repackaging of the exe-- and if it still occurs now, it is a lot easier to detect and notify the script author about the license violation.