Possibility to transfer with call waiting disabled

Hi,

When using Yealink SIP Phones I can receive more than one call in my SIP account.
I want to disable call waiting, so that if an extension calls me and I'm occupied the phone states that. But, if I disable call waiting I can no longer transfer any call.
Anyway I can prevent the phone from receiving calls when I'm on talking but still be able to transfer any call ?

Best Regards,
João Raposinho