How to get confidence intervals using CFtool when setting bounds on coefficients

Hello, I am currently using the Curve Fitting tool to get a curve fit on my histogram. I am using a custom equation that requires a lower bound of 0 for the only parameter (I have only one parameter coefficient). This allows me to get an accurate curve fit, but the cftool no longer gives me 95% confidence intervals on my parameters. Is there any way to fix this? Thanks, ~Monica