There is thread solving similar problem. It is about charts but I think you should be able to do the same with gauges. Try to look at http://thwack.solarwinds.com/message/58095#58095 and let me know if it helps.
Aha! That's brilliant! Thank you so much for the link.
Did you ever get this working? I've found with this method that graphs work fine, but with gauges I just get a broken image link, have tried various bits of the HTML but no joy sofar.
I'm trying this with IP SLA Round Trip Time Gauges
EDIT: After some further investigation I've found that this works fine with utilisation gauges for network interfaces, but will not work with IPSLA RTD gauges. This has something to do with the live nature of the gauge graphic. I've managed to get it to display momentarily when it was at 15ms, but as soon as the figure changes it breaks the image. I suspect that each gauge reading is generated on the fly by solarwinds then the link is binned when the RTD changes.
If anyone manages to get this working with IPSLA gauges I'd appreciate an update!