I found out that both Foobar2000 and MP3Tag both supports some limited command line operations, and with a tiny bit of legwork, you can add a right-click (context menu) way of making this process easier.
With this approach, you can now right-click songs, select a context menu option and Foobar2000 will automatically apply ReplayGain at the track-level then MP3Tag will automatically open up and add the songs ready for you to apply the custom Action we previously created.
First, make sure you have Foobar2000 and MP3Tag installed.
Second, copy the following script and put it in a batch file and save it somewhere you can remember. I put mine in E:\Documents\ReplayGainScripts\ReplayGain.bat. I’m on an x64 system, so notice the environment variables highlighted in red which will need to be changed to %PROGRAMFILES% if you are on x86 (32-bit).