Position at central workspace on login

I have set up 3x3 workspace switcher, and I want my position to be on the central one by default. Is it possible?

Thanks to Marco, I have figured out a way using wmctrl.

Because compiz workspaces are actually viewport of a single desktop, so the solution is to move the current viewport to cover the center region of the desktop.

First, call wmctrl -d to get the information of current desktop:

read desktop_id _ast \
    DG_ geometry \
    VP_ viewport \
    WA_ wa_off wa_size \
    title \
    < <(LANG=C wmctrl -d | grep '*')

geom_w=${geometry%x*}
geom_h=${geometry#*x}

# The workarea size isn't accurate, because the top/bottom panel is excluded. 
viewport_w=${wa_size%x*}
viewport_h=${wa_size#*x}

rows=$((geom_w / viewport_w))
cols=$((geom_h / viewport_h))

# Fix the viewport size
viewport_w=$((geom_w / rows))
viewport_h=$((geom_h / cols))

Then, calculate the origin of the center viewport:

center_row=$((rows / 2))
center_col=$((cols / 2))

center_x=$((center_col * viewport_w))
center_y=$((center_row * viewport_h))

center_viewport=$center_x,$center_y

And move the viewport there:

wmctrl -o $center_viewport

Yes: install wmctrl

sudo apt-get install wmctrl

and create a file in ~/.config/autostart/wmctrl.desktop with the following:

[Desktop Entry]
Name=Desktop Switcher
Exec=/usr/bin/wmctrl -s 4
Type=Application