I totally agree that a diode may be the best choice.I am quite aware of a transistor being able to function as a diode, BUT for this application, a diode with adequate ratings should be simpler and probably less expensive, and certainly easier to get the correct connections than using a transistor. Diode voltage and current specs are simpler to understand, and that may be a benefit to those who are not extensively experienced in the field..
BUT, the TS specified that he is limited in the components he has available. AND he has stated specifically that he does not have a diode. HENCE, using a transistor as a diode is his best choice.