If he is not an existing member ( an employee who joins your establishment after leaving an employment where he was a member of PF but before withdrawing his PF accumulations) why should you cover him under PF. If your company policy says that every one irrespective of salary should be covered, then it is okay but if you do not give PF to all employees and when there is a ceiling put on employer's contribution to PF contribution, it is advisable not to cover an employee whose wages is more than Rs 15000.
Now, in the case of piece rate wages, since there can be a month in which his wages may come down and he would be under PF coverage anyway, then cover him with with a wages of not exceeding Rs 15000 so that there will be contribution towards Pension fund also. The Act does not make it mandatory that Pf should be contributed on the entire amount earned but it can be restricted to the prescribed percentage (12%) of Rs 15000. Therefore, even if the wages is Rs 17000, you can deduct PF on Rs 15000 and contribute employer's share to PF as well as Pension Fund.
Madhu.T.K