I think You have a very low chance of getting banned.
I have bought and used 10+ pins and I still have 0 blackmarks. And I have never heard that anyone would have been banned for that.
Very low i think the chances of getting caight are like 1/100. they only way they could find out who got that pin, and i don't thik they'll go through all that trouble.
The only difference is that the payment is coming from a different IP address, which is no where near enough evidence to do something against your account.
Plus, Jagex makes money either way, so they couldn't care less.