How can I customize the Guest user Dock in Yosemite? How can I customize the Guest user Dock in Yosemite?

Here are a few approaches I've tried but haven't been able to complete:


In past versions of OS X, you could customize the Guest user Dock by putting a plist with your desired configuration at /System/Library/User\ Template/English.lproj/Preferences/com.apple.Dock.plist. In Yosemite, it seems this plist is overwritten by the user creation script.
I've created a Profile Manager configuration profile with my desired Dock layout, but I can't figure out how to add the profile to the Guest user. (Logging in as Guest and enrolling doesn't seem like it would work because the configuration would be erased at logout, and even when I try it, I get the error that the user isn't allowed to add or remove configuration profiles.)
I've tried modifying my Guest account, then copying the entire home directory to /System/Library/User\ Template/English.lproj/. This does modify the Dock, but it also results in Keychain permission problems. It also feels like a very heavy-handed solution to modify one configuration.
I'm currently exploring creating a script that will remove all the Dock icons and add the ones I want when the user logs in. This doesn't feel like a great solution, since it has to run on every log in. I'm struggling right now with how to set the configuration to get the script to run on login.


If anybody else has any ideas, especially if you know or have an idea about how to keep the user creation script from overwriting the Dock plist, I'd be very grateful. 

Thanks!
Right after posting this I thought of another approach. It's not perfect but it's the best I've come up with, and it mostly works.

After copying my desired configuration to /System/Library/User\ Template/English.lproj/Library/Preferences/com.apple.Dock.plist, I ran chflags uchg /System/Library/User\ Template/English.lproj/Library/Preferences/. (I'm not sure why the flag needs to be set on the Preferences folder, rather than on the plist file itself, but that's the only way it works.) On logging into the Guest account, my customized Dock was intact! The only problem is that the user creation script still adds icons for Maps and iBooks, but that's not the end of the world. 

If anybody else has any other ideas, I'd love to hear them. I want to believe there's a better solution, but at least I've got something that works now.