We've had the same problem [bundling/load balancing of several ADSL lines] of switching
the IP-adress during exam sessions.
The only permanent way to view the results [using the html-userinterface] was to modify and recompile the
"Wimslogd/score.c" file [comment out: /* strcmp(ip[i],wlist[4])==0 && */]
Another more troublesome way is ofcourse to ask the systems administrator to unify/modify all IP-adresses in the class score-files on the server, every time after exams...
The good news is: although the scores may not be visible in the html userinterface, there is no dataloss in wims !