It sounds super juicy, but I think ralph is right, and it comes back to the relationship you might have with the client. This is similar to the tactic I ended up doing - over-estimating the CAD hours, talking to the client about what I’ll be doing, and reiterating that the goal is to not use all the time/hours listed. The CAD budget thus becomes “do not exceed” and if there is indication that we will, we have another conversation about why, and how much.
Breaking up the CAD into smaller bite sized portions “a la carte” for the client also seems to work - its easier to budget hours that way.