TOC Link to Non-RH Help

I have web-based help (HTML5 responsive with RH 2017) and one of the TOC links points to a non-RH system, like this:

Is there a way to open that link inside of a new browser tab using a TOC RH property or attribute? Or do I have to do an actual .htm with a javascript redirect?

I tried adding a target="_blank" attribute, but that only works on .htm pages, not inside xml like the .hhc is.