Hi Max Fraser,
1. You could move the logic in a custom/user control and then drop it on a page. This will allow you to edit the content of this page within Sitefinity.
2. You could add your aspx to a folder of the website root. Then, from the backend create a page of type "External" and link to your physical aspx. By doing so this page will be added to the SiteMap and your SiteNavigation, but you will not be able to edit the content of this page in Sitefinity's page editor.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.