thank you Stefan,

Use that path as
option to --with-sysconf-dir=

that means, when compiling the radius at installation?

to Ivan Kalik:

Best advice - don't do that!!! Certificates are *much* safer on a server
than on a USB device - what are you going to do if someone walks off
with it?

:) yesss I'm with your advice, but if the usb device is a smartcard, it becoms other thing.. the problem is that I must understand what are the inpout/output of this device to reach it and extract the information..
ouuf, lonng road!! :(