Have you seen this chip?
Tilt Compensated Compass Breakout - LSM303DLMTR - SEN-10888 - SparkFun Electronics?
"LSM303DLMTR Breakout Board - Tilt Compensated Compass"
Sounds kinda like what you're after: "a tilt compensated compass using the HMC5883L compass and the ADXL345 accelerometer"