Increasing Serial Buffer for AVR8 USART

[Flavan]

I've been trying to use the LUFA library to emulate a controller and want to send data to it via UART serial communication on a Teensy 2.0++. I was trying to use Teensy's UART library (https://www.pjrc.com/teensy/uart.html), but there seems to be some conflicts with the LUFA library and instead of reading the communcation, modifying the input and outputting the modified data, it just spits back the same data. I then found LUFA's own USART peripheral (http://fourwalledcubicle.com/files/LUFA/Doc/151115/html/group___group___serial___a_v_r8.html), but it doesn't have a built in buffer more than a few bytes. I'm new to C and chip programming, so I'm not sure how to go about adding a larger buffer to the peripheral in order to store the amount of data I need (just ~16 bytes at a time). Any help would be much appreciated. If anything needs more explaining, let me know and I'll do my best to explain.