You can specify a window's position by editing $HOME/.config/openbox/lubuntu-rc.xml.
Back-up lubuntu-rc.xml as a safety measure.
Open $HOME/.config/openbox/lubuntu-rc.xml with a plain text editor.
Scroll down to the section titled <applications>. You'll see a lot of text commented out.
Immediately after the last commented line, paste the following:
<application class="Lxterminal" name="lxterminal">
<position force="yes">
<x>-0</x>
<y>0</y>
</position>
</application>
Save lubuntu-rc.xml (as a plain text file).
Open a terminal and run openbox --reconfigure. There should be no error dialog window indicating parsing errors, etc.
Now, when you run lxterminal, it should open at the top right corner of your screen. Once you're sure, lxterminal opens as specified in the example, edit lubuntu-rc.xml to adjust the x and y values to suit your needs remembering to run openbox --reconfigure to make the changes register after saving your edits.
You can consult http://openbox.org/wiki/Help:Applications for more details.