Urgent! How can I thaw a turkey that is partially frozen that has to be brined by 8AM

after thawing my 15lb turkey in the fridge for 5 days, it is still mostly frozen. I usually brine it overnite, in icewater in the fridge. I have to have it in the brine by 8AM tomorrow morning. I understand that to fast-thaw, you put it in ice water and change it every 1/2 hr. I'm wondering if I can use the frozen state of the turkey as part of the "ice" in the brining water, and just let it continue thawj g it in the fridge tonight, and put it in the brine tomorrow, even if it is not completely thawed.