Short answer is: you can't use uninstalled fonts with Pango. :(
Longer answer is: you can, if you are using the fontconfig backend (PangoFc; eg on Linux). In that case you need to make a few calls to fontconfig before using Pango, to make the fonts available to fontconfig. However, I don't think Fontconfig has Mono bindings.
So, I'm afraid you're out of luck here.