If you can't provide audited accounts - you need to provide one of the other alternatives:
(h) One of the following documents must also be submitted:
(i) The organisation's latest annual audited accounts with:
(1) the name of the accountant clearly shown; and,
(2) the accountant must be a member of an accredited accounting body specified in paragraph 19 (g)(ii) of Appendix A of these rules;
(ii) A certificate of VAT registration and the latest VAT return confirming the VAT registration number, if turnover is in excess of £73,000;
(iii) Evidence to show appropriate planning permission or local planning authority consent is held to operate the type/class of business at the trading address (where this is a local authority requirement); or
(iv) A franchise agreement signed by both parties.
It would suggest you need audited accounts - overkill or not.
You could try to use the following clause:
If the applicant does not submit the document(s) as requested, the caseworker may refuse the application. Where the specified document(s) cannot be supplied (e.g. because they are not available in a particular country or have been permanently lost), the caseworker has discretion not to apply the requirement for the specified document(s) or to request alternative or additional information or documents be submitted by the applicant.
But I really doubt that most ECOs are going to see many applications from sole traders and I'm willing to bet most wouldn't understand the difference why audited accounts would be uncommon for a sole trader.
I personally, if you're worried, would get the accounts audited.
M.