Launch programatically without actual error

Is there a programmatic way to launch the error page?
Say, from a different middleware?

I'm working on a [debug helper Rack middlware](https://github.com/Arachni/arachni-debug-rack) and I'd like to pass a custom exception (in order to provide my own binding) to better-errors and have the screen accessible via the usual `/__better_errors` location.

I've been digging around in the codebase but got somewhat lost so any help would be appreciated.

Cheers