In order to create a Google Account without signing up for Gmail service, visit https://accounts.google.com/signup and pick "I prefer to use my current email address" option. After filling the form and confirming email, you can then add that newly created Google Account to each of your Search Console services.

On your computer, go to Gmail. Enter your Google Account email or phone number and password. If information is already filled in and you have to sign in to a different account, click Use another account. If you get a page that describes Gmail instead of the sign-in page, at the top right of the page, click Sign in.