Nothing. The G31/G41 is an entry level, economy chipset with, as you found out, a very limited FSB freq. My G41 is a little better than yours. The FSB freq limit is 352 MHz. The motherboard just will not run at 353MHz.
That means that Core2 CPU's with a 333 MHz FSB freq are not good candidates if you are trying to OC with a G41. CPU's with 200 MHz - 266 MHz FSB freqs work better as you have more overclocking headroom.
One of my G41's has a 2.93 GHz E6500 in it happily running at 3.66 GHz (333 MHz X 11). That particular chip will run at 4 GHz in my old P35 board.