How to Accomplish

I'm working with the Sparkfun Serial backpack on a graphic LCD. The standard text is to small for one of the things I'm attempting so I have to make a larger font. I'm setting up routines to draw sections of a number like a segmented display so that I can individually call them as needed but to make it work i need to be able to offset them by a specific value. So I need to find out how to take a decimal number and convert it to a hex format to be used in the following syntax.

Serial.print(0x31, BYTE);

I've got a routine that will figure out the hex value and store it in an array. Just need to know what to do from there so that the correct Hex value is being sent to the LCD.

So I need to find out how to take a decimal number and convert it to a hex format to be used in the following syntax.

Why? That command would work just as well if you sent it 49 instead of 0x31 (3*16 = 48 + 1 = 49).