Recently it has been observed that the transport of conserved charges into the electroweak bubble wall alters the spontaneous baryogenesis scenario, by allowing the baryon asymmetry to be generated over a larger volume including the outside of the bubble. We give here a very simple analytic estimate of the change in the baryon number generated, by considering a simple toy model with a single particle and a single conserved charge. Our results indicate that in general diffusion itself will produce at most a small enhancement of the baryon asymmetry as compared with the original spontaneous baryogenesis scenario; by no more than a factor of order 10. This suggests that any large enhancement of the baryon asymmetry due to diffusion effects in realistic multi-particle models can only be due to the elimination of cancellations between the contributions of the individual particles. Our discussion should be generally useful for making simple estimates of the baryon number generated including diffusion effects, given the asymmetry generated in the original spontaneous baryogenesis model.