CHDK doesn't provide a way to do this while shooting with the normal Canon controls. According to the manual, the continuous with AF and LV settings reduce the shooting rate to 5.7 and 5.9 fps respectively, which might be close enough if you can accept having one of those features active.
You could enable raw, which would probably bring it down to a bit over 1 fps. Canon raw is generally a bit faster than CHDK. Or you could invest in really slow SD cards 🤣
In CHDK, you could do it with a shoot hook script with an approach similar to what I used in the contae script
https://github.com/reyalpchdk/chdkscripts/tree/main/src/contae
That script doesn't control shooting rate, but it does provide an example of a script that "passes through" most controls while also using shoot hooks. For your use case, you'd need to add a minimum delay to with hook_shoot and remove the exposure stuff.
