I would humbly suggest that the answer to spills and general dispensing issues, though probably not to the paint drying out, can be found by googling Droptop by Dr Tabletop.
P.S. For the benefit of those of a suspicious mind, I should add that I am not Dr Tabletop; nor am I related to him or in any way affiliated with his business other than as a backer of his Kickstarter for the Citadel bottle tops. I understand he has since launched a similar project for Tamiya paint jars.
I can also offer assurance that the lids are well manufactured and work as advertised. I assume they are now on general sale. Given the obvious need for something to address the problems highlighted above, I would certainly hope so.