Posted this solution in another thread:
One work around you can do is change the "name" field (NOT the "username" field) of any entry, and add an ascii character like an exclamation point '!' to the front of whatever one(s) you want to appear first.
For me at least, LastPass always sorts alphabetically by the name field, regardless of favorites or usernames. You can further choose sort order via different characters. You can find a list of the character sort orders here: http://support.ecisolutions.com/doc-ddm ... _chart.htm