Hi Barbara,
I have 2 extremely picky boys, ages 13 & 6. My oldest boy will not eat any dish where a veggie us detected or raw. My 6 yr old boy will eat some veggies, only raw though.
With my 6 year old I have always given him a side of ranch he can use as a dip, and given names that work for him... Such as instead of "broccoli" we eat "baby trees" ( he gets a kick out of that one ) cauliflower is smarty balls ( I tell him eating veggies makes him smart & he always thought it looked a little like a hard cotton ball ) I have also explained that our bodies are like cars, mommy has to put gas in the car to make it go and stay healthy, and our bodies need foods like veggies to keep our bodies happy and healthy. He eats carrots for me because I've told him they help give him good eyes. He is my easy one when it comes to veggies, he actually gives issue eating red meat! You can also sing songs about eating veggies, for example, the tv show "Yo Gabba Gabba"(Nick Jr) sings a song about eating carrots & green beans. They wanted to join the "party in my belly" - you can also look that up I think on " you tube" searching "Yo Gabba Gabba" (just make sure you watch you tube things first)
Now my 13 year old I have to be creative and sneaky! I sneak at every opportunity!! None of the things I mentioned above EVER worked with him! With him, I sometimes make meals that call for veggies but purée them, I have also taken muffins and such & mixed in puréed baby food. ( he won't even eat a salad of any kind no matter what the dressing or plain! ) He will take a bite and chew just so as he inspects the food to see if I have added any veggies! Now I should also mention he is my "texture" kid. If he does not like the texture of the food he won't eat it. Now if I do make something that has veggies or is something "he thinks" he won't like, or rule is "3 bites" before rejection. Even if he rejects it, he at least gave it a chance, and eventually his tastes will mature and (hopefully) accept more foods/veggies.
Other ideas beyond sneakiness, and taking into consideration the age of your son, is make pick up a veggie you want him to try and start eating it near him. Exaggerate how delicious it is and the hold it out and watch, but say something like "nobody better try to take a bite of my delicious _______!" IF he goes for this, turn to see someone had taken a bite, look around and say "Hey! Who took a bite?!" Sometimes that will work. Key word being sometimes!
Another idea is to "make" edible things from them. Cucumber butterflies (cucumber slices with a sliver of carrot in the middle) celery boats (celery with cream cheese or peanut butter down the center with raisin people) Get creative. Sometimes this is a good way to get them interested in trying.
I'm sure you will get many great ideas!! Good luck!! If you need more info on anything I've mentioned, recipes or idea-wise, feel free to message me. :)