When I was in the Marines, we'd rub it directly into our covers (lids, hats, caps) and dry them on a block.
One option is to by a concentrated liquid starch like Sta-Flo. I usually dilute this 6/1 with distilled water. I put this into a spray bottle, and give my shirts a good squirt prior to ironing. (Tip - its usually best to spray the entire shirt, roll up, and then start ironing. This allows the starch to penetrate into the fabric, so you don't get the "flaking" that occurs when a hot iron touches liquid starch.) I usually keep the spray bottle handy and give collars, cuffs, and placket an extra spray to keep them looking crisp. This ability to vary the quantity of starch over different areas is a big plus to the "spray liquid" approach.