Not worth the trouble to make one yourself.
Just get the
"Big Boy" clutch stop available from UUC Motorwerks for
$20 (as shown below). It's a good, solid design and works great.
Note that the E39 probably will not start
with a clutch stop installed. The starter lock-out switch requires more
travel than is provided with the stop in place.
The easiest way to get around this is
to apply several small adhesive-backed felt pads, like the type that
typically are used for furniture legs, to the flat area on the arm that
engages the switch.
Just jumping the switch is easy, but probably
not a good idea since it keeps a relay under the dash "hot"
while the switch is activated and may cause problems since the car's
systems will think that the clutch is depressed all the time (e.g.,
cruise probably won't work properly).
A better way would be a simple circuit
to momentarily activate the switch on start and then cut out. I'll post
an example here when I can.