GOTO a specific address in HI-TECH C Compiler PIC18F
This is the kind of thing most easily done in assembler.

If you need to do this regularly, you can create a assembler subroutine that follows the C subroutine linkage conventions.  This would take a 24 bit argument that is the address to jump to.  Remember to have the subroutine pop its own return address from the stack before doing the jump.  The subroutine would write bits 23:16 of the address to PCLATU, bits 15:8 to PCLATH, and then bits 7:0 to PCL.  That last instruction will actually do the jump, so everything else needs to be set up properly before the write to PCL.