plink-ng | comprehensive update to the PLINK association analysis | Code Analyzer library

I'm in the process of making a singularity container with PLINK v 1.9 (a genetics software, not the PuTTY interface, https://www.cog-genomics.org/plink/1.9/dev) inside it. I'm able to successfully compile the software within the container and I can see the PLINK files and functions when I shell into the container. To make things easier for my end users, I am trying to add the software's main folder to the singularity $PATH so that they can just call plink from the command line, but I'm not able to achieve this.

So far I have tried:

1. Assigning SINGULARITYENV_APPEND_PATH=path/to/plink in the %runscript section of my singularity recipe file.
2. Moving the source code folder for Plink into /usr/local/bin of the Singularity
3. Setting a variable PLINKDIR=/path/to/plink and the export it in the %environment section of my recipe file similar to what they have done here.

None of these methods work. The only way I can access this package is by spelling out the full path in my singularity exec command.