Disable one portion of JavaScript?

Most online banking sites will log you off after X minutes of  
inactivity for security reasons. However, my bank is Washington  
Mutual, and instead of logging me off, they pop up an annoying  
JavaScript alert! So, if I do some banking, then switch to another  
app for awhile, OmniWeb's dock icon will suddenly start bouncing up  
and down because of some stupid JavaScript code on WaMu's site. I  
have to stop what I'm doing to close the dialog box so that OmniWeb  
will stop bouncing. (Or, if I'm viewing another tab, OmniWeb will  
immediately switch to the WaMu tab. I think that's actually a bug  
from a HIG standpoint, which disallows focus-stealing.)

Anyway, this is all quite annoying. I've tried disabling JavaScript  
for the WaMu site, but because they use JavaScript for other things,  
that ends up making the whole site non-functional. I was thinking I  
might be able to use Greasemonkey to disable just the part of the  
code that displays the dialog box, but of course Greasemonkey only  
works with Firefox, not OmniWeb. Is there some other way of handling  
this problem? Thanks,

Trevor