@Ph**
, WOW, I have never seen that :O , usually the primary person gets a year extension and then the trailing spouse gets a matching extension.
I would say IF you both have year-long, multi-entry Non-F visas and all you can get is 90 day extensions from the immigration office at a time just forget it.
It's way better for you to hold the visa you have (which is unlimited entry/exit into the country for the validity) and just border bounce every 90 days to get another 90 day stamp until the visa runs out.
The near land borders to bangkok are Poi Pet & Ban Laem Cambodia, and Phu Nam Ron in burma out in Kanchanaburi. Or you could fly out and back in too.