Certainly managing the witness votes of multiple socks is easily done using proxies. All the socks could simply proxy to accounts that each vote seven witnesses, and all the VP the owner spread through all the accounts would be cast for 30 witnesses in total, if that's what they wanted to do. However that VP would be split and only approximately 1/4 would apply to each witness (28/7 = 4), so it would reduce considerably the stakeholders ability to vote his entire stake for 30 witneses.

1 Steem 1 vote does so 4 times more.