[wp-hackers] domain/main to domain - WP network

[A5D]

Just a quick question as my head is spinning …

Client currently has a WP network installed at:
domain.com/main

Now, if I create more sites on this install they will come out as:
domain.com/main/site2
domain.com/main/site3

etc

What I actually need is:
domain.com/main
domain.com/site2
domain.com/site3

The 'root' has to stay as domain.com/main as that's how their host has set it up and they won't budge.
Confusion reigns and I can't see the wood for the trees and am sure I'm simply over thinking this and it's actually very easy to sort.

Suggestions as to how to achieve this please.

TIA.