I have a 6 1/2 foot female who was eating colossal rats from rodentpro so I decided to try a small 1 lb rabbit. She is normally an aggressive feeder but didnt really seem to show any interest. I wiggled and jiggled it with tongs to no avail. It was not too large for her. I gave her a rat and she ate it instantly. I thawed out another 1 lb rabbit next feeding day and rubbed a rat on it and she gobbled it right up.
I agree that you may be forcing a little too much for a 4 1/2 footer, and you definately should not be feeding live rabbits. I wont even feed live mice unless completely necessary. They may never get hurt, you dont know, but if s/he'll eat frozen thawed- go for it. At LEAST prekilled and use tongs...
It also has a less chance of bacteria, bugs, etc...
Good luck, and I dont know how big your boa is, only that its about 4.5 ft, but if jumbos are not enough, maybe try a colossal rat before jumping to rabbits.
Good luck,
Nicole
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Nicole Gustafson
Coal's Constrictors (formerly Coal's Cold-Blooded Creations - changed to simplify and there is another 'Cold Blooded Creations'...I'm not trying to hide from anyone or anything! 
Cook Minnesota
BOAS:
Gavin, Lydia, Hailee, and Jade ~ Dumeril's
Wyatt, Sheena, Shaylee, and Mary Jane ~ Columbian
Desdemona ~ Peruvian
Madeline ~ Surinam
Avery ~ Bolivian
CORNS:
Kiana and Sierra ~ Amel
Casper and Kissa ~ Anery
Tripp and Scarlet ~ Bloodred
Aidan ~ Ghost
Skylar ~ Anery Hurricane
Ariel ~ Striped Amel
Lily ~ Blizzard
Ambur ~ Creamsicle
Neva ~ Snow
Sage ~ Normal
BEARDED DRAGONS:
Divine ~ Silver Pastel
Christopher ~ Sandfire Red x Sandfire Yellow
Baby ~ Snow
CAT:
Morgan ~ Calico Tabby
DOGS:
Maximillion Vasco von Katzel and Len-Mar-'s Lexed Leas ~ AKC German Shepherds
HORSES:
Mateo ~ Palomino Paint Quarter Gelding
Chic ~ 3/4 Quarter 1/4 Arabian Bay Mare
Rayna ~ 7/8 Quarter 1/8 Arabian Palomino Filly
Dallas ~ Palomino Quarter Gelding
Banner ~ Red Dun Quarter Mare
Chance ~ Buckskin Dun Quarter Stud Colt