With sky is very hard because the mac is hardcoded on the router/modem by the isp.
You get loads of different ips whenever you reset the modem or router which makes it very good for ebay/paypal muti accs. But since you cant change macs makes it useless for amazon.
It is still possible to change mac on sky router but is a bit complicated and i will not go into that...
I would suggest switching providers or do like me - i have both virgin+sky broadband in my house :) - broadband packages are very cheap and for the sales i make is pennys..
- i use virgin broadband for multi amazon accs on my pc
- sky broadband for multi ebay/pp accs on my laptop | 
