gdevilspie works for me on Mint 14 Cinnamon (though I have spoken to others that claim it doesn't work for them). That is supposedly capable of launching apps on specific workspaces, but to get that to happen through autostart would not be so easy. You would have to put a long delay into the autostart command in order to allow gdevilspie demon to start before the application is launched. You could probably do that through a shell script and then launch the shell script through 'Startup Applications'. I wouldn't feel confident about giving you the code for that though, do a bit of research and you can probably work something out.
Gdevilspie is in synaptic/software center.
Fujitsu Lifebook AH532 Laptop. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Ubuntu12.10 (Unity), Mint14 (Cinnamon), Manjaro (Xfce).