Mt.Gox is no problem.

Define a new withdrawal method OKPay in your withdrawal section, enter your OK Pay wallet ID, in 24hrs they will verify that you are trying to withdraw into a valid OKPay account and then the OKPay option will appear in the withdrawal section fo ryou to use straight away.

All the normal withdrawal limits apply though - if you are looking to trick the system, its not going to work :-)