The administration of drugs integral to a procedure is always incidental to any service that requires them and cannot be reported separately. The infusion codes are bundled to the procedure codes and can only be paid if submitted with a modifier to indicate that they were unrelated to the procedure, e.g. a separate and stand-alone therapeutic drug administration that was not part of the procedure itself. This is true not just for stress tests, but for any surgical or diagnostic procedures that involve administration of drugs, contrast materials, or other fluids. Since the Regadenoson is only for the purpose of the stress test, the administration would not be eligible for the modifier.
This is addressed throughout the CMS NCCI manuals, but specifically to this situation in Chapter 11, section I 10: "Cardiovascular stress tests include insertion of needle and/or catheter, infusion/injection (pharmacologic stress tests) and ECG strips (e.g., CPT codes 36000, 36410, 96360-96376, 93000-93010, 93040-93042). These services shall not be reported separately."