On WebLogic 11G I can use the console to set the FrontendHost and FrondendPort on a server or on a cluster so that re-directs are handled correctly and end up resolving to the front end load balancer instead of the local host.

The MBeans associated with this on WebLogic are, for example:

MBean Name  com.bea:Name=AdminServer,Type=WebServer,Server=AdminServer
Attribute Name  FrontendHost
Description The name of the host to which all redirected URLs will be sent. If specified, WebLogic Server will use this value rather than the one in the HOST header.
Sets the HTTP frontendHost Provides a method to ensure that the webapp will always have the correct HOST information, even when the request is coming through a firewall or a proxy. If this parameter is configured, the HOST header will be ignored and the information in this parameter will be used in its place.
Type    java.lang.String
Readable / Writable RW

How is the same thing achieved under Websphere 7?

Follow up info:

So I have 2 use cases actually.

One is that I have a web app running under WebSphere on host A on port 9002 and a LB running on host B at port 80, when I visit the home page of the app via the LB on http://hostb/app the app redirects my browser to http://hostb:9002/app and it 404's

I think this is WebSphere's fault but I guess it could be the app's fault?

The second is that the web app in question needs to send emails containing URls that the customer can click on to get back into the web app - obviously this needs to be via the LB. On WebLogic the app uses MBeans to derive the LB url and I was hoping to use a similar mechanism on WebSphere.