Andrew Woolley/AP PhotoThe Cubs have an impact bat waiting in Iowa if they can make room for Anthony Rizzo.

As we saw at the end of April, sometimes it takes an injury for even a prospect like Bryce Harper to get an opportunity in the big leagues. For Mike Trout of the Los Angeles Angels, it took a combination of an injury (Vernon Wells) and a release (Bobby Abreu) to get him consistent playing time in Anaheim. Sometimes the combinations can get even more complicated, such as in the case of Will Middlebrooks. Despite Kevin Youkilis' return from the disabled list, Middlebrooks has stayed in the big leagues because of the positional switch he made from first base to right field to stay clear of the Boston Red Sox's best hitter, Adrian Gonzalez.

They're hardly the only ones, as there are plenty of top-flight prospects in the upper levels of the minors who deserve a shot soon, but figuring out how that happens requires some out-of-the-box thinking. Here are four premier prospects who are currently blocked, including solutions for clearing their way to the big leagues: