[Theme: Radiate ] fixed header image for certain pages

Hello communety

I′m currently having randome Pictures in the header of my theme.

My problem is that I want to have a fixed header image on certain pages. But the once I do not have a fixed image should still be random.

I tried some Plug-ins but they did not work properly. I ended up still having the random header images and a fixed image just underneath the header image which locked really stupid.

I hope you got an idea of what i′m trying to do ??
Thanks for your help in advance