Removing the 'Server' response header with custom error pages

Hi,

I was reading through this thread while looking at how to remove the 'Server' HTTP response header on 404 pages: https://forums.iis.net/t/1233506.aspx?How+to+remove+Server+Name+Microsoft+IIS+8+5+from+HTTP+headers+ 

The problem I'm having is that the solution he put forward (switching the httpErrors existingResponse attribute to 'PassThrough') breaks the use of custom error pages for us.

Can you advise on how to sort this?

Thanks

James