Keyboard and Mouse sharing before login with OS X Yosemite

Are there any solutions available that would enable sharing a mouse and keyboard connected to a Windows machine (specifically Windows 10) with a Mac running OS X Yosemite before the Mac has been logged in? I have been trying to get Synergy to work for a while now, but it seems that (if I can even get it to run prior to login) it gives me error messages evidently resulting from lack of access to the window system (This post suggests that it may be a sort of bug in synergy, and I remember the synergy website once outright stated that starting before login was not supported). Are there any other options that would not suffer from the same issue, or is OS X Yosemite simply too locked down to allow this sort of thing?

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