Is it possible to set up routing on App Engine in the Google Cloud balancer?

Question

Google Cloud Platform

I tried to set up HTTP(S) routing through the balancer.
For example:
Serve static content from Storage at https://mydomain.com/* , and upload it through the App Engeine instance that I want to host here - https://mydomain.com/upload/ .
However, only Instance Groups and Network Endpoint Groups can be selected - everything is Compute Engine specific.
But what about App Engine?