Here are some of my waypoints from the salar. They include some directional ones (go south here) and these are for a trip from uyuni to San pedro. You can of course reverse the direction and you should include them anyways since they may help you.
here you can get my garmin database with the points and my tracks
Having the wanderlust mapset greatly helps you.
Arbol De Piedra S22 03.109 W67 52.992 4585 m
Bol Aduana S22 26.452 W67 48.353 5019 m
Bol Border S22 52.434 W67 47.426
Camp Ende (gas,water,food,accomodation) S22 10.415 W67 49.117 4316m
Chilean aduana+border S22 54.665 W68 11.629
Colchani-Entry to Salar S20 18.001 W66 55.999
Waypoint EntrytoSalar south (approximate,but you cant miss it) S20 33.995 W67 34.499
followtracksouthhere S21 04.831 W67 59.809
San Juan (gas,water,food,accomodation,incagraveyard) S20 53.930 W67 45.915
Geyser S22 25.988 W67 45.704 4885 m
go south to here and follow railway S20 58.589 W67 45.934
go straight S21 23.609 W67 59.617
Hot Spring S22 46.945 W67 48.168 4330 m
IsladePescada(approximate) S20 09.956 W67 45.154
keep left S21 30.535 W67 51.695
keep south S21 44.924 W67 58.644
Laguna Blanca S22 32.140 W67 38.980 4422 m
lago colorada S22 09.692 W67 44.950
laguna verde S22 47.113 W67 46.591