Well, if you created a new setting with new_url as the varname, then you could use {vb:raw vboptions.new_url}. To create an option you can temporarily turn on debug mode for your site, then go to the settings in the admincp, go to the group you want to add to, then click on the "Add Setting" link that will appear at the top of each group. You can also create a new setting group if you want (there's a link on the main option page).
Here's an article about turning on debug mode, if you aren't familiar with it:
https://vborg.vbsupport.ru/showthread.php?t=265999