protected void Page_Load(object sender, EventArgs e)
    {
        //Initialises my dirty hack to remove the leading slash from all web reference files.
        Response.Filter = new WebResourceResponseFilter(Response.Filter);
    }

public class WebResourceResponseFilter : Stream
{
    private Stream baseStream;

    public WebResourceResponseFilter(Stream responseStream)
    {
        if (responseStream == null)
            throw new ArgumentNullException("ResponseStream");
        baseStream = responseStream;
    }

    public override bool CanRead
    {
        get { return baseStream.CanRead; }
    }

    public override bool CanSeek
    {
        get { return baseStream.CanSeek; }
    }

    public override bool CanWrite
    {
        get { return baseStream.CanWrite; }
    }

    public override void Flush()
    {
        baseStream.Flush();
    }

    public override long Length
    {
        get { return baseStream.Length; }
    }

    public override long Position
    {
        get
        {
            return baseStream.Position;
        }
        set
        {
            baseStream.Position = value;
        }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        return baseStream.Read(buffer, offset, count);
    }

    public override long Seek(long offset, System.IO.SeekOrigin origin)
    {
        return baseStream.Seek(offset, origin);
    }

    public override void SetLength(long value)
    {
        baseStream.SetLength(value);
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        //Get text from response stream.
        string originalText = System.Text.Encoding.UTF8.GetString(buffer, offset, count);

        //Alter the text.
        originalText = originalText.Replace("/WebResource.axd", "WebResource.axd");
        //Write the altered text to the response stream.
        buffer = System.Text.Encoding.UTF8.GetBytes(originalText);
        this.baseStream.Write(buffer, 0, buffer.Length);

    }