Preference for managed servers?

Hi

I was wondering if it’s possible to configure a cluster with a particular
proxy server using some managed servers until they fail before using others.

Example scenario:

There is one weblogic domain consisting of 6 managed servers. Two server are
located in the US(usms1,usms2), two in the UK(ukms1,ukms2) and two in
Sweden(sems1,sems2). To access the cluster users go via a software load balancer
(HttpClusterServlet or similar). 3 Instances of the software balancer exist, 1
in each of the countries above. 

Question:

Can you configure the software load balancers so: if the request comes from the
US software load balancer (slb) that it uses the usms1 and usms2 all the time
unless they both fail in which case use any from the remaining
(ukms1,ukms2,sems1,sems2). Like wise on the UK slb configure it to use ukms1 and
uksm2 until they both die and then use any of usms1,usms2,sems1,sems2. The same
thing again for Sweden.

We do have another way of doing this by creating 3 domains with a cluster of
just the two managed server and failover to the other domains via some higher
level hardware devices (not a load balancer) but this involves a short period of
“outage” which it would be nice if we could avoid by having the one cluster
then we only use the hardware to ‘failo