301 on multiple domains

[w_s_o]

Most of my clients have their own servers, but I have a smaller customer who just uses a shared hosting plan (on an IIS server) and has one main domain and then about three others that he wants to just forward to that main domain.

So I know the best way to do this is with a 301 redirect, but from all that I've read, the only way I know to implement that is to buy hosting plans for each of the other three domains and implement the 301 on each. Is there a way to forward those domains (appropriately) to the main one without having to buy hosting for each?

Thanks!

[goodroi]

Some domain registrars will provide this service for free.

[JoeT321]

Which ones?