The occurrence of an (n+m) input operand instruction that requires more than n of its input operands from an n-output data source is recognized by a programmable vertex shader (PVS) controller. In turn, the PVS controller provides at least two substitute instructions, neither of which requires more than n operands from the n output data source, to a PVS engine. A first of the substitute instructions is executed by the PVS engine to provide an intermediate result that is temporarily stored and used as an input to another of the at least two substitute instructions. In this manner, the present invention avoids the expense of additional or significantly modified memory. In one embodiment of the present invention, a pre-accumulator register internal to the PVS engine is used to store the intermediate result. In this manner, the present invention provides a relatively inexpensive solution for a relatively infrequent occurrence.