I haven't heard of one for paypal and implementing it would be difficult enough I'd say..
i'd reckon your problem is that LT isn't liking the link as it's a cmd link (or java essentially) the security will be stripping it
I think theres a setting in the admin that allows js to be posted ....
edit: yeah it's in admin under security
Don't know how if or how it may help you though.. maybe you could link an external .js file such paypal_link.js - use the script tag to include that file and it may work...
not sure other than that though..