The source code can be downloaded here:
http://open.litespeedtech.com/packages/openlitespeed-1.4.25.tgz
In a terminal:
1. Extract the tarball
2. cd into the new directory (openlitespeed-1.4.25)
NOTE: you could skip 3 and 3a first if you want to make sure that compiling works before editing anything.
3. The file to edit is openlitespeed-1.4.25/src/main/plainconf.cpp
3a. Roughly at line 1182, there is the line
const int MAX_LINE_LENGTH = 8192;
change 8192 to something bigger, e.g. 16384 and save.
4. In the terminal again, run ./configure
5. Once configure is done, run make
6. If compilation succeeds, just mv the openlitespeed-1.4.25/src/openlitespeed binary to the bin directory wherever your installation is (default will be in /usr/local/lsws/bin/)
I will be out of work in 15 minutes, but I can reply to any questions tomorrow morning if you run into any issues!