I'm not sure there's another way to enable the LCD screen without enabling it in the firmware. You might be able to edit something in the EEPROM, but I'm not sure with Marlin (usually that's the type of thing that you compile in, in my experience).
I'm guessing your board came with firmware already on it? -- Honestly, if you want to do anything that's not "out of the box" with your printer (like adding an LCD screen, or auto-bed leveling, etc.) you're going to have to get used to editing your firmware. In my experience, it's not really something you can get around.
Tom has a pretty good video guide on configuring and uploading the Marlin firmware for RAMPS (and yeah, it's "Marlin", not "Merlin").
Edited 2 time(s). Last edit at 04/09/2015 08:22PM by BrainSlugs83.