Assuming temperature is a word size variable and holds a value of 1578 (for 15.78 deg C)

Use SEROUT2 with the DEC modifier. (See Manual Section 5.71)
(SEROUT doesn't support modifiers)

Also have a look at Manual Section 4.17.7
DIG will solve your problem

Code:
SEROUT2,Pin,Mode,[DEC1 temperature DIG 3,DEC1 temperature DIG 2,".",DEC1 temperature DIG 1,DEC1 temperature DIG 0," °C"]
You will have to add the control-codes for your LCD to the code-example