Since Darwin lacks lesskey (see herehere and here) I installed less 458 via MacPorts and added the bindings using the defaults path for my system. lesskey will take $HOME/.lesskey and output $HOME/.less. You can also use LESSKEY or LESSKEY_SYSTEM.
~ $ vi .lesskey
#command
\n forw-screen
\40 forw-line
~ $ lesskey
~ $ ls -d .less*
.less .lesshst .lesskey