You can try but I very much doubt it will work.
Also, if your brother already has or is moved to Digital Voice, he will need the SH2 for it to work.
By the way, just got around to testing this, on the SH2 ive connected the WAN Port to Eth3, and now I have a solid orange light which was previously pulsing purple.
So there you go, it works on the SH2.