Rovers swooped to capture Sharp on transfer deadline day from Sheffield United, agreeing a loan deal for the 23-year-old striker until the end of the season.
"He is one of those players we've looked at ever since he was at Scunthorpe," O'Kelly told the Sheffield Star.
"We've envied the side (Sheffield United) that he plays for because he's a natural goalscorer.
"When he played at Scunthorpe he had the ability to play up front in a pair; he could also play on this own.
"Everything about the boy fits in with the way we play and how we do things, and we are really pleased to have got him for the season."