using xyplot with groups and panel.linejoin

Dear All,

I am using xyplot() with many groups like this:

statselect <- levels(dat$stat)
xyplot(relmse~T|lambda, groups=stat, data=dat,
       panel = panel.superpose,
       key=simpleKey(statselect, lines=T))

However, I want lines not scatterplots and if I set
panel.groups=panel.linejoin that connects the lines according to the
relmse and not according the consecutive values of T. Is there a short
solution to this very simple problem, which doesn't require custom made
panel function?

Thanks in advance,

Kati