You can also try using a cat bag. You can purchase them online, for your cat I'd recommend the large size. Just fasten the velcro around his neck, then tuck him into the bag and zip it up. Then just unzip at the spot you want to pop the fluids in. Generally even the most uncooperative cats give up once they're in the bag, they know they're good and caught. Lots of petting and praise while he's in the bag and offer his favorite treat.

If you can't find a proper cat bag you can improvise with a pillow case. And switch to 18g needles if you're not already using them, the fluids fly in much faster. Good luck with him.

Kimm