The way I've understand your diction of "Business English" is the english used in business.And if I've got that right,the following would be my speech.
The difference between business English and colloquial English is simply the choosing of words.And how do we enhance our oral ability so that we can speak fluent,professional Business english?My ways are to practice,practice,and practice.
What else could one do,when encountering a new language,so that one can master the foreign language but to practice?Practicing can be simply broken down into speaking,writing,and reading--elements invovled in learning a language.And learning Business language is the same thing.One could practice speaking the language to his/her peers to improve oral skills.And one could write,using business English to his/her boss so that Business language can be spread,and exchanged.Reading business english allows one to learn and see more of the language used in the business field.And among the three approaches of learning,the most important would be reading.Reading business english is probably the only way one can speedly increase one's vocabulary,comprehension skills,and writing.
-sorry if it's not enough.this is the best i can do-