I was checking the Grooovy Download site
http://code.google.com/p/groovyarcade/downloads/list and noticed a NoMechanical.diff file to Delete Mechanical Games from MAME.
Although the NoMechanical.diff file did not work for me I was able to manually edit the src\mame\mame.lst file.
In the src\mame\mame.lst file the mechanical games fall below
/* Drivers below are _mostly_ mechanical games, usually with no video display, requiring external artwork to function. */
and in-between
/* [BEGIN] fruit machine drivers */
and
/* [END] fruit machine drivers */
and also in-between
/* [BEGIN] pinball drivers */
and
/* [END] pinball drivers */
Delete all the driver names between those [BEGIN] and [END] sections and recompile.
Building MAME without the mechanical drives saves about 6 Gigabytes of disk space when using clrmamepro to Scan and delete the now unneeded ROMs.