Bing Webmaster Center currently offers a number of methods you can do this by...
... but the easiest way to achieve this on SupaDupa is by adding a CNAME to your DNS records.
What to do:
Log into your Bing Webmaster Center account
Click on the Home tab
If the site is not already added, click on Add Site and follow the onscreen instructions.
if already added, click on the Verify Now link next to the site name.
... a pop up box will be displayed showing you the different options available ...
Click Option 3: Add CNAME record to DNS
... follow the instructions given on how to add the CNAME details to your DNS records ...
Once you have added the required CNAME record to your DNS settings, log back into your Bing Webmaster Center account
Click on the Verify Now link next to the site name
Click on the orange Verify link
.......and that should be it.
To use this method, you must be able to sign in to your domain registrar or hosting provider and add a new DNS record.