That seems like a real problem,,,, having a 2003 SL and all !!!
I agree with bobterry99, modifying the remote circuit would be your best bet. It won't be easy though, the circuitry is probobly surface mount technology and with all the encoding it is a very sensitive piece of equiptment. If your willing to spend a few hundred dollars i'm sure the modification is possible.
Good Luck!
Adam

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320