[yocto] Different patches for different images for same machine

[Andreas Eipeldauer]

Hi,

I have extended the basic images core-image-minimal and core-image-full-
cmdline to images that differ by installed items in the rootfs, like core-
image-minimal-web has dhcp-client, inetutils-telnetd, openssh openssh-
sftp-server installed.
Now I would like to customize the environment variables in u-boot with 
patches and create a dedicated u-boot to the appropriate image.

Any advises how the most robust realization for this would be?

Should I create a dedicated Machine conf instead of different images, or 
is there a way to conditionaly add an additional patch to u-boot ?

Thanks for helping me out, greetings Andi