Instructions
Open the armor list and scroll down to the armor you wish to equip.
Scroll down to the bottom of the armor list. Count up the number of armor suits from the bottom entry to the one you wish to equip.
Push the X button to bring up the upgrades screen. Press Y and immediately push and hold the A button.
Select "No" in the option that appears after the Turn into Omni Gel screen automatically disappears and is replaced with the armor list.
Scroll down to the bottom and count up the number you counted in Step 2. Equip the armor that is there, and you will find that you are wearing the armor you wanted in Step 2.