How to use custom runtimeconfig.json from LinqPad?

I've recently started getting an error "System.Drawing.Common is not supported on this platform" when trying to use the EPPlus Nuget package. I only get this error when loading our application's library DLL into LinqPad which references EPPlus to generate an Excel file. I found this page which seems to explain the error:

https://docs.microsoft.com/en-us/dotnet/core/compatibility/core-libraries/6.0/system-drawing-common-windows-only

However the fix involves adding a setting to the runtimeconfig.json file:

"configProperties": {
  "System.Drawing.EnableUnixSupport": true
}

How can I access the runtimeconfig.json file used by LinqPad or use my own?