I do not work in BW but in ABAP Transaction SM59 is where you would set up your RFC connection. Here is a sample piece of code to use the RFC. The code does not work, I just threw something together. d_system would be defined in your RFC.
CALL FUNCTION ‘Z_RUN_PROGRAM_ON_ANOTHER_BOX’
DESTINATION d_system (This is your RFC)
credat_low = credat-low
credat_high = credat-high
return = wa_return
i_temp = temp.