Parametric Worst-Case Execution Time (WCET) is a static analysis that computes a WCET formula that depends on various parameters. The formula can be used off-line for fast parameter space exploration, and on-line for adaptive scheduling. In this work, we propose a technique that, by static analysis of binary code, automatically produces a formula that represents the WCET of a procedure as a function of the procedure arguments. The formula captures how the control-flow, and thus the WCET, depends on the argument values due to arguments appearing in branch conditions (loop conditions or if-then-else conditions). We use the TACLeBench benchmark programs to illustrate the impact of procedure arguments on the WCET. Our tool generates C code with bounded WCET that can be embedded in the analysed program to evaluate the formula on-line. We show that, for some programs, the potential gain is significantly larger than the cost of evaluating the formula, thus opening the possibility of adaptive scheduling.