Transfer secondary account to new N7 ?

[YOuichi]

Dear Forum,

I've had a Nexus 7 for over a year, and my son has had a secondary account on it. I've recently purchased a new Nexus 7 for him, and would like to transfer his apps/save gems etc onto his new Nexus 7 as the primary account, but can't seem to find a way to do this.

I've tried the Helium backup, but this only seems to work on the primary account.

Is there any easy way to do this ?

Thanks in advance,
Youichi