I tried your trick earlier using my Pansat 3500 which has been updated to use Pansat's version of diseqc 1.1 and 16 LNBFs.
I had mine set for diseqc 1.0 and tried hooking up an LNBF to port 1, 2, and 3. I got signal on port 1, but none on ports 2 and 3.
I then switched to Pansat's version...