That's probably your best bet. I have the Mars Light obsession too, and have installed the Ngineering modules in a number of 3rd Rail engines. GRJ's methods are undoubtedly more efficient than mine, and I haven't attempted - because it was never necessary - to use these modules in an MTH engine.
The Ngineering Mars Light Simulator requires an onboard DC power supply, which you can get from Ngineering, but it's an incredibly small separate module and requires some soldering effort to install. (I don't say soldering skill, because despite my best efforts I don't have any!)
The Lionel/MTH approach to this feature has not been consistent. I have found the latest versions of the Lionel effort, including in a VL GS steamer, less than convincing. In certain TMCC models, they did it 'way better. This is a very short video of a Santa Fe F3 from about 2003:
This is a conversion of a 3rd Rail E7 diesel I did a few years back. I think that 3rd Rail now uses the Ngineering modules in their 3-rail models:
Yes, the Ngineering version is far superior, it actually looks a MARS light! I think the only real way to scratch this itch is to have a pro install it for me.