Shortened IEEE citation?
The best practice is to follow the IEEE citation style.

Having said that, in a conference paper there is going to be a lot less strict check of the actual format of the references you use and I doubt a paper might get rejected because of that. Worst case, you will be asked to correct them either during the review process or when the proceedings are being compiled by the conference organisers . 

For journal articles, these will be formatted by IEEE so you do not have a choice.