Generally this is done with DFII environment variables in your
.cdsenv file.
asimenv.startup projectDir string "~/simulation"
Replace "~/simulation" with your path.

You can do this also in the .cdsinit file with
envSetVal( "asimenv.startup" "projectDir" 'string "~/simulation" )

This has as side effect the advantage that you can evaluate
UNIX environment variables with SKILL e.g.

t_projectDir = getShellEnvVar( "PROJECT_DIR" )
t_projectSimulation = strcat( t_projectDir "/simulation" )
envSetVal( "asimenv.startup" "projectDir" 'string t_projectSimulation )

A good way to figure out which DFII environment variable is affected
is to write a .cdsenv file before and one after the specific value
is set in the GUI and the do a diff over the two files.

Bernd