Update: Evidently it is a made up word. From an interview with Variety -
“I have a friend who calls himself Dr.Lacubrious,” Mraz said. “He’s like, it means lazy, its another word for lackadaisical. We couldn’t find it anywhere, and one day he left a message on my machine, and he’s like, you won’t find it in the dictionary because I made it up. And I thought it was very appropriate, because it is based on a friend of mine who’s the king of one-liners, who’ll say anything to get what he wants. And he’s usually pretty smooth about it.”
Found this info on this person's Site.

www.newleavesinmarch.com/2003_03_01_archives.html
by Chevy May 8, 2005
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easy to chill out or hang out with. jason mraz uses it in one of his songs.
"i can be lacubrious with you"
by jess June 15, 2004
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la·cu·bri·ous
Pronunciation: la-'cü-brE-&s also -'cyü-
Function: adjective
Etymology: irregular derived with a positive twist from lackadaisical created in 1994
1 : Chill Out; especially : exaggeratedly or affectedly becoming less tense or reserved < " I can be lacubrious wit' you." – J. Mraz>
2 : Relaxed <a lacubrious feeling>
Idioms be at ease, breathe easily, feel at home, make oneself at home
- la·cu·bri·ous·ly adverb
- la·cu·bri·ous·ness noun
- Dr. La·cu·bri·ous title
by Anonymous September 20, 2004
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