You could modify the PFD to omit the dispute portion.
However, I don't recommend it.
A PFD is basically a goodwill gesture between you and the creditor. If you owe money and they don't accept a PFD (and they don't have to accept), then your letter may be seen as an admission of liability that you owe. Nothing would stop them from then suing. Far-fetched? Nope, I've read a small number of cases like that happening.
In fact, a DV first is recommended. Not only are you challenging it, but it gives the CA an opportunity to lay out the exact cost for which you can PFD later.