Best practice to create differential ouput pair

Hello,

What's the best practice to create / define a differential output pair on Cyclone III dev board. This is for a LVDS clk output. Unfortunitely, I cannot use the dedicated clk output pins, since I'm driving the clk to a daughter card that expects the clk on certain pins.

I have used the ALT_OUTBUF_DIFF in the past, but it has be suggested to me that this is unnecessary. Is there a way to do it in the assignment editor?