You might be able to play some 'tricks'. The LCD won't respond to anything on it's pins unless the ENABLE pin is low. Hopefully, you have HSEROUT connected to a DATA pin or the R/W pin.
HSEROUT takes over a in when the port is enabled. Set SPEN high, Transmit your byte(s), wait one byte time for the last byte to be transmitted, and disable SPEN. Put a resistor between TXout and your MAX232. Connect an unused pin (call it the "blocking pin") to the junction of the resistor and the MAX232. Drive the pin high as soon as you get done transmitting the last byte, and tristate the pin before you send any data. Setting the blocking pin high will stop any garbage from going out on RS-232 while you write to the LCD.

So, before you send a character using HSEROUT

Tristate the blocking pin
Enable SPEN
Write the data
Wait one byte time
Set the blocking pin high
Disable SPEN

I haven't tried it, but it just may work.