An old documented way of preventing services from starting immediately after installation in Debian/Ubuntu is using the RUNLEVEL environment variable to trick the runlevel helper into returning a response that the system isn't fully running, such as:

# RUNLEVEL=1 apt-get install nginx

Sadly this doesn't work in newer versions …

At this point Ubuntu 14.04 Trusty Tahr is nearly 2.5 years old, with another 2.5 years support left until it reaches end of life for support. However for those of us still working with Trusty, it's often desirable to try and get a few backported modern packages …