It's a tricky thing to do - use something as cliched as "boo hoo hoo", or try to write the sound, like "uh huuh huuh"? (My example could also be read as laughter). Perhaps it's better to follow meow's suggestion and describe how the dialogue is presented: "I'm sorry!" he said, crying. "I'm sorry!" he cried tearfully. "I'm sorry!" he sobbed.

no, I do not think so ) IMHO you may try something like "aaaaaaaaaaaaa!" or "eeeeeeee!" or it will be better to use remarks such as [crying], [sob sob], etc.