Ive tried adding a subdomain through cpanel which contains a dash e.g. alan-reid.splashhost.com
but it just adds alan, has anyone had the same problem and knows a fix for it?

Alan:

I have seen that once or twice myself.

You need to go into the httpd.conf file and make the change. Once that is done, all should be working.

is there a fix for cpanel for it though? i dont want to have to it manually every time a customer wants a sub domain with a - in it

Not that I am aware of, but in reality, it is not a hard process. Most clients do not put dashes in them. I have seen only a couple out of the hundreds that I have done. Dashes are not very professional, considering that it is a subdomain and there is not that much of a need for dashes.