I did a quick dealer seach from the www.bmwmotorcycles.com
Looks like you don't have much of a choice. My suggestion, get a disney annual pass so you have something to do while your bike is in service. There might be an independent mechanic closer, but I don't know of any.
Here are the results:
50.0 miles MALCOLM SMITH MOTORSPORTS 7563 INDIANA AVE.
RIVERSIDE, CA 92504 (951) 687-1300 Map Directions
61.7 miles BMW MOTORCYCLES OF NORTH COUNTY 499 HALE AVENUE
ESCONDIDO, CA 92029 (760) 520-1288 Map Directions
70.7 miles BROWN MOTOR WORKS, INC. 885 W. MISSION BLVD.
POMONA, CA 91766 (909) 629-2132 Map Directions
73.8 miles IRV SEAVER MOTORCYCLES 607 W. KATELLA AVE
ORANGE, CA 92867 (714) 532-3700 Map Directions
80.7 miles BRATTIN MOTORS 4952 EL CAJON BLVD.
SAN DIEGO, CA 92115 (619) 286-1971 Map Directions
92.7 miles LONG BEACH BMW 2998 CHERRY AVENUE
SIGNAL HILL, CA 90755 (562) 427-5494 Map Directions