Under 18 with premium access, linking accounts?

[shippothekit]

I won the 30 days unlimited access from the contest and was wondering if I could link accounts with my sister so she can have unlimited access too. I tried using the guide here but the link accounts button doesn't show up on either of our accounts because of our ages. Is there any way to link our accounts so we can both have premium access?

I tried making another account over 18 and linking it to both of our accounts but only mine was premium and the rest stayed basic.

Is there any way to do this or is my sis stuck with basic? Thanks.