Why don't you give the mobile number ? Its not like the registrar has access to your mobile number, only google would know the accounts you have registered with them for a specific cell number.
And i realize google can see the registered email in whois then realize your cell number's registered emails used for different registrars but i don't think any algorithm can do that and if it comes to a manual review, you're fucked anyway.
If you are that paranoid, use aol, hushmail and countless others email providers out there.