If you plant a kiss on him, you're really putting yourself out there. If he's not interested, you run the risk of direct rejection, which can be painful and hard to recover from - it sounds like you guys have a great relationship and I would hate to see it ruined over a single action.
Find other, more subtle ways to initiate contact.
- When you're listening to music, touch him casually on the arm, or even better on the leg.
- When you're walking or standing, 'accidentally' brush up against him.
- Prolong your eye contact with him - hold his gaze for an extra second or two.
If he's not interested, he may not respond to your actions, but you have not put your self in a position to be absolutely rejected. Make sense...
You can just go back to the way it was before if he doesn't respond.