You can use DTT (dithiothreitol), it smells bad but not as bad as BME. I'm unsure if it's as effective; we use it in combination with protein-based RNase inhibitors (RNaseOUT).
Beta-mercaptoethanol is a reducing agent that irreversibly denatures RNases by reducing disulfide bonds and destroys the native conformation required for enzyme functionality. However, like Laura Leighton said, DTT (dithiothreitol) has also been suggested. Exposure to the toxicity and pungent smell of beta-mercaptoethanol could be avoided by using hand gloves, full face mask with type A filter, face shield for eye protection and protective clothing for skin and body protection. Therefore, there are ways to go around the toxicity and pungent smell of b-ME and not replce it. But then, can beta-mercaptoethanol be judiciously and effectively be replaced by DTT? Please see the attached document: Article Replacing β-mercaptoethanol in RNA extractions