cannot tell anything about the bookmarks plugin (dev stuff), but if you only want to get LastPass working and if the only prob is storing a script snippet, macros sure can help.
lastpass.com also requires permission for 3rd party cookies and https-referers.
The current version of the "light" macro is here, discussion should also be continued there:
If there's still a length prob, your bookmarklets could simply be hardcoded in the macro, if you edit the kmm-file manually. Or could be stored in a separate file alongside it.