Bute doesn't have to be a fight - my Arabian used to trot over to the gate to slurp it out of a 60 cc syringe. Everyone else was mad 'cause he was getting "treats". Some critters hate it more that others, but maybe these ideas will help you out.
Some people have told me I was nuts for coddling my animals, but it's a lot easier on me to mix up a bowl of goodies than to catch, then fight with, an upset horse. Not to mention that mine never figured out he was being "tricked" - he just figured I was in a really generous mood for a few weeks and bringing him treats all the time.
Method #1 - Goop in a Syringe:
(First, either get powdered bute, or get a mortar and pestel.)
Jam the end of the 60 cc syringe into a raisin, so it cuts a little plug that acts like a cork. Stand the syringe up between 3 soda cans, or something. Pour the bute'n'goodies mix into the syringe - use a rubber scraper to get all of it. Put the plunger just barely in (so you don't pressurize it), and flip it over. Let the mixture drain to the plunger end, so the air is in the nozzle end. Remove the raisin, or just start pushing the plunger' til it pops out. Once you have the plunger securely in, head to the barn.
You might want to give several "doses" without bute, like any other treat, and don't catch and tie the horse if you can avoid it (so they don't get the idea that "something's up".
Cooper used to just say aahh and slurp it up.
If he isn't already scared of syringes, try getting him to think they are the bringers of good stuff - coat the end of one in one of the above delicious kinds of goop, then let him lick it off, work up to squirting just plain syrup into his mouth every so often as a treat, then just sneak the bute in from time to time. :-)
Method #2 - Bowl of Goodies:
Another technique I used was to mix bute into a yummy snack, and feed it out of a stainless steel bowl, while I was watching, to be sure he got it all. Try some gooey combination of shredded carrots, syrup, shredded apples, bran, raisins, oat-mo, etc. and just mix the powder in so he has to eat it along with the goodies.
You might want to make up enough for all your horses, but only put bute in the for one who needs it. If you do, make sure the each eat only their own bowlful.
Grate several carrots (like for carrot raisin salad).
Add any of the following:
Make up quite a bit, to make it harder to taste the bute. It's a lot easier to grate 2 more carrots than it is to fight with a horse that doesn't want to eat something. Make sure it's pretty sloppy - no chance of picking the bute out of this mess. If the horse will accept it, it'll be the easiest thing in the world to feed. I used to make up 3 stainless steel mixing bowls of this every night, and give one each to Sabrina, Eeyore, and Cooper (his had bute), just to avoid fighting. I think there is something compelling for a horse about watching his/her buddies snarfing down their bowls of goodies that convinces him it's a good thing. I'd also try to feed it right before meals, when he was less fussy, as long as it was food.
The less fighting you can have, the better off everyone is - your horse won't dread seeing you with a syringe or bowl, and you won't be giving off those sneaky, I'm here to cause you trouble vibes. I never had to catch Cooper for either of these - just show up at the gate, and hand over the goods. If you can get your horse in that habit it'll be really easy for a groom to handle it. Maybe pack it in a tupperware or ziplock bag, and the groom will just have to dump it into the special "treat bowl". :-)