HelpURL with relative directory

With the HelpURL attribute I can link my own components to a custom documentation url. I want to them to open a local html file inside the project folder. I can do so like this:

 [HelpURL("file:///C:/Users/Name/ProjectName/Assets/Documentation/page.html")]
 class ClassName : MonoBehaviour {
     ...
 }

This works perfectly fine, the problem is, it only works for my specific setup, as the path given in the HelpURL attribute is absolute. Is there a way to link to a relative path?

Using Application.datapath doesn't work, as it needs to be a constant. Simply inserting a relative path like so:

 [HelpURL("/Documentation/page.html")]

also doesn't work.