A replacement dual LNBF is about the same price, or even less than a 4x4 switch. A dual LNBF will give you independant reception on both boxes.
A local store here has the DMSI JSC322 0.3 dBdual LNBF for $20.00, but a Zinwell 4x4 multi-switch is $28.99, so it is cheaper to just replace the LNBF itself. You will have to run a second coax line to your second receiver.
The only single output LNBs that can distribute both polarities to multiple receivers are stacked LNBs such as those found on the Dish Network Superdish. While these allow great flexibility, they also introduce the complication of stacked frequencies, with the horizontal transponders added above the vertical ones.