Free Shipping + fee if cash on delivery

Hi.
I want to give free shipping if the costumer pays by bank transfer over 150€ (that I have managed with the free shipping module), the problem is that if the costumer choose the option cash on delivery I want him to pay a fee of 3€. The shipping is still free but he has to pay for the cash on delivery expenses.
Is it possible?
How can I do that? By changing the free shipping module? Or by duplicating it and made some changes? I've spent hours thinking but don't know how to do it.

Thanks in advance

You can add a fee for a specific payment method using Payment-Based Fee/Discount. You can then use your shipping methods as normal, although note that the shipping step comes *before* the payment step, so you can't really give Free Shipping when only bank transfer is selected, because shipping will have already been chosen.

Thanks for the reply Johnathan, but I was searching for either a free extension or a code to make possible this option. Maybe my post was in the wrong forum, I don't know.

No, you're not in the wrong forum. I was suggesting my extension because I don't know of a free extension to do this, but you can search the extension store for that option.