Unfortunately every slicer is different. I assume you're using slic3r, which I believe has a pretty obvious way to accomplish what you're asking for:

http://manual.slic3r.org/expert-mode...l-optimization
I would set it to 1mm^2.

Why though? Why not let it infill the small area? If it's because of over extrusion...well, that shouldn't be a reason (properly fix overextrusion).