Control over build process

Hi,

Is there a way to have control over the build process?

I am using custom_ci_worker example to build my image, however it fails to be pulled by kubernetes because of the out of space error. My theory is that intermediate layers take too much space. During the build I download 10Gb of source code, compile my binaries and get rid of the source code eventually, but since it's distributed over several RUN commands, intermediate layers get preserved and take all that space. What I want to do is to squash them together, using docker's --squash, but I don't have access to the build command.