All IRAs are considered together regardless of where they're held, so you might get away with it for a time, but this is absolutely against the law and if you get caught (which seems likely) you'll have to take corrective action which will involve taking the money out, paying penalties and will be a pain.
Do you have a workplace retirement plan, or are any self employment income? Your workplace plan might allow you to roll the IRA in, or if you have self employment income you could open a solo 401(k) that would allow you to roll the IRA which would open the backdoor up to you.