The simple answer ...
Select only Clients that agree in writing at the outset that they confirm Contract is outside IR35, and have a term in the contract that requires notice from them if they want to change their mind with the option of the contractor company to immediately terminate the contract in that eventuality.
I don't think an individual can unilaterally be compelled to become an employee (with or without employment rights) without providing their informed consent.
That would be something akin to slavery and forced labour. Arbeit Mach Frei.