365 Business pre-setup , 365 ignores MX records

Hi there

365 Buseness , I need to pre-setup on several new PC's , and prep for moving email to 365 Exchange Online (email to be moved early Jan)The issue is, 365 exchange ignores MX records , for other 365 companes email to another 365 based email domainSo I cant pre-setup user & email a/c's in advance . What will happen , is any email from other companies using 365 will go to my pre-setup email a/cs', despite mx records pointing elsewhere .

Any good ideas to work around this ? I need to add user a/c's to be able to install Office365 on new PC's to be delivered onsite early next monthI dont want to create a mess by using @onmicrosoft a/c's & changing them later to login with real email a/c (not sure if that matters?)

I cant risk adding the domain name to the 365 a/c in advance, as it would auto add it to Exchange & theres the real risk of 365 ignoring mx records before theday of the email changeover to 365

Any good ideas about how to manage this ?cheers