There is no boolean value as such, but you can set originalUrlAsQueryString to "true" in the 51Degrees.config file.
"If set to true the redirected URL will have the original requesting Url
encoded and included as the origUrl query string parameter in the
redirected Url. This will enable the mobile home page to determine the
original requested resource providing the option to display a mobile
friendly version. (Optional – defaults to false)"