Any HW or FW Requirements to add a second antenna on 'AUX' connector?

Hallo,
I would like to ask whether anybody knows which are the requirements (both Firmware And/Or harware-capacitors, resistors, conectors, cables) for Asus WL-500g Premium in order to connect another external antenna to the free 'AUX' connector of the PCI plate inside?

Any requirements to the antenna too?

Thanks for your suggestions. I am eager to test any working solution.
I am using now as external antenna a Linksys 7dBi one.
I am using now the original Asus FW: 1.9.7.5.
I have also 'repaired' the R17 fault of the WiFi plate. It is OK now.

Thank you in advance.

brgds
AlexPPC