Hmmmm... my thoughts:
Light bondage - no spread eagle-ing at this point! A blindfold might be good.
Use a safe word and explain what it means: If he really needs the tickling to stop, he's panicking or having some physical problem, the action STOPS, no exception ever. Unless you hear the word, however, let him know that his pleading "please stop" might get you to stop.... or it might not! Keep him off guard by both occasionally granting and ignoring his pleas for leniency. Appeal to his macho masculine side and let him see this as something like getting 'hit' in football- it's a challenge, a test to see how strong he is, how much he can take.Threaten him that if he uses the safe word too much that he'll be like the boy who cried wolf and you'll have to punish him (don't ACTUALLY punish him - the safe word is there for a legit reason and should be used when necessary, but let him know he should use it only when he means it).
Make it pleasurable for him. Mix in the tickling with some kissing, hugging, etc. so he eventually associates tickling with pleasure and trust.
Start slow, and make it light. Spice it up now and then with fast, intense "no mercy", "I'm gonna get you" tickling, but keep it mild for the first few sessions. You can always step it up a notch in later sessions if he takes a liking to it. Keep it fun - make funny faces and use funny voices. It's less scary to a new person when you don't seem so serious about it, and it makes it more of an adventure to a curious guy...
Affection! Affection! Lots of it!
Dominant streak? Don't avoid the bad spots. Find one, and tickle him there until you make him tell you something you want to hear, or perform some kind of act or little task for you (kissing your toes, make him confess a dirty secret with you at the center of it, etc...) At that point, he gets a break. Reward him for his cooperation.
If all else fails, I'll be happy to demonstrate!
You are going to have so much FUN!