Final answer:
Catheterization is the recommended sterile technique for urine collection when cystocentesis is not viable, as it minimizes external contamination.
Step-by-step explanation:
The method of urine collection recommended for a sterile collection when a cystocentesis cannot be performed is catheterization. Bladder expression and free catch are not typically sterile techniques, and amniocentesis is a procedure unrelated to urine collection, as it involves sampling amniotic fluid. Catheterization allows for a urine sample to be collected directly from the bladder using a sterile catheter, thereby minimizing contamination from external sources.