Im would guess theres a plugin for SV that would do this but I would do the following which might be a bit long winded and not correct but it will do the job.
Assuming your using HD 1920 x 1080
Get all 9 videos each on a different timeline (stacked one above the other)
Resize them all to the same size
width = (1920 / 3 = 640 - 10px for the 2 borders)
height = (1080 / 3 = 360 - 10px for the 2 borders)
Then position the 3 central videos starting from the middle one and working up and down then left and right
Otherwise what has just sprung into my head
using something like photoshop make a quick template (ie the image above to mate the
output size assuming 1920 x 1080
drop this on a timeline
shrink all the videos to fit the boxes
remove template from timeline