Name Server

I'm having issues with having my registrar change my primary NS to office365 NameServers. At the same time, I pay to have complete control over my advanced DNS records, so ideally I only want MX records to go to office365, not all of my domain requests. Is there anyway to tell office365 setup to allow the office 365 NS to be 3 and 4 instead of 1 and 2? I would like to keep my primary and secondary NS with my registrar, and add the Office365 NS after those, as well as the MX records. Does anyone know a way to do this or a work around? My registrar seem to have 'idiot proofed' their DNS interface so if I even log into my advanced DNS settings, my primary and secondary NS are reversed to their defaults - not the office365 NS.

Thanks - and I hope there is a way to do this.