On the following non-linear least squares estimation of the risk parameter (risk), I would like to additionally impose the restriction that estimated risk parameters should be lower or equal to 1. Is there any way to do this?

Code:
nl (bid=privatevalue-(({risk=0.02}*privatevalue^((N+{risk}-1)/{risk})-{risk}*reserveprice^((N+{risk}-1)/{risk}))/((N+{risk}-1)*privatevalue^((N-1)/{risk}))))