You should be able to do it by editing the configuration file. The instructions for configuration are in
http://openbox.org/wiki/Help:Bindings
http://openbox.org/wiki/Help:Actions
So, if I understand it (no guarantee!), to move the current window to the left and make that the active desktop would be
<keyboard>
...
<keybind key="C-A-S-Left">
<action name="SendToDesktop"><to>left</to></action>
<action name="GoToDesktop"><to>left</to></action>
</keybind>
...
</keyboard>
That's the sort of thing which deters me from using Openbox or LXDE!
Incidentally, I use W-Left to move focus to the left window and W-Home to shift the program to it: much less finger stretching.