Custom app_index.html with bokeh serve apps

It took me a while to figure out that when serving multiple bokeh applications using, for example:
bokeh serve src/app1/ src/app2/ --index=template_name.html
the template_name.html should be the absolute path, so in order to make it work the command should be:
bokeh serve src/app1/ src/app2/ --index=/absolute/path/to/template.html

Is this the only way to do it while still using bokeh serve?
I have the feeling that there is a more straightforward way that I am missing.

my directory structure is:

   |    +---app1
   |    |       +---templates
   |    |       |       +---index.html
   |    |
   |    +---app2
   |    |       +---templates
   |    |       |       +---index.html
   |    |
   |    +---app_index.html

I have the applications running on heroku for the moment, so, in this case my Procfile is:
web: bokeh serve --port=$PORT --address= --use-xheaders src/app1 src/app2 --index=/app/static/app_index.html

Bokeh just passes the value you provide to Tornado directly as-is in a route specification, so it’s really about what Tornado expects or can use. I don’t happen to know offhand. Assuming you are executing bokeh serve in the project directory, I would have tried --index static/app_index.html (i.e. the relative path from the current working directory of the process). But if that does not work then absolute path is probably the only option.