WebService JS proxy is not cached

I have several JS proxies generated on the page through using code like:
scriptManager.Services.Add(new ServiceReference("~/Service.asmx"));
 
This code generates the following JS proxy on ASPX page where it is used:
<script src="../../Service.asmx/js" type="text/javascript"></script>


 
This file is not being cached in browser cache. I checked in firebug and in header it says:
Cache control: private
 
All other JS and CSS files are being cached with "Cache-Control: public,max-age=8640000".  In web.config I have:
    <staticContent>
      <clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="100.00:00:00" />
    </staticContent>
 
How can I get JS Proxy files to cache? ...