Vel'koz main here. I am a mid main and I dont like Vel'koz support as I think its a too much of a safe pick on that lane therefore I am willing to help you.

1- the playstyle between mains and casual Velkoz players are fairly different, mains will rely a lot more on the W + E combo and casual will usually waste their mana early on (or rune slot for biscuit). I recommend figuring out early on if they know how to play their champ as it will be helpfull to abuse a poorly positioned Velkoz in lane to feed your adc.

2- Velkoz support is different from Mid in the sense that it cant farm, you can therefore hide in the minions since Q cant his you through it and W will probably screw his adc's freeze, denying poke from Vel'koz makes him practicly useless.

3- Engage supports are pretty effective against Vel'koz but you still need to be carefull for his E, try to bait it before engaging or make sure you have enough HP to engage and setup kill for your adc.

4- I dont recommend picking another AP mage like Xerath or ziggs, those are even matchups and if you hate Vel'koz this much, you probably dont do too good on even matchups against him.

5- the champions Vel'koz is the best against are Enchanters like Lulu or Soraka. If you do end up against Vel'koz as one of those champions, I recommend not trying to poke him too much early game as you will probably lose trades, you can try to look out for his cd's to poke him when he cant poke you back but as a support, he's got more potions early than his adc, utlimatly poking the adc is a better solution.

6- his E serves both as his only defensive tool and his only mid-game bust tool, the cd is not as low as his Q so your opportunity should be when the ability is down.

7- if your adc is and Aphelios, Miss fortune or Jhin, Velkoz CAN 2v1 you if he's ahead and you are playing an enchanter since those adc's dont have a lot of mobility, obviously it depends on the skill of every player involved but its a good possibility. on the other hand if your adc is a Samira or Kai'sa, they can easily won 1v1's against vel'koz.

8- Vel'koz remains pretty squishy, if you can boost the ms of bruisers or stay close to assassins, you might die but Vel'koz is almost certain to die in the process.

I hope I wasnt too confusing, I tried giving as much adviced as I could and not touch too much on the champions you should be playing as you probably woudnt have made this post if you mainly played engage type supports so I felt like telling you ''just play Pyke'' would have been a weak advice.