IMU where Accel & Gyro have different sample rate

I have an IMU where the Accelerometer has an update rate of 400Hz, and the Gyro of 380Hz.
I would like to use an orientation filter such as the ones by Madgwick or
Mahony, but they expect to get the data from the 2 sensors simultaneously.
What could I do to fix the problem, without introducing complex sample rate converters?
Would duplicate 1 gyro output in every 20 (MCD between 400 and 380) samples work well, or introduce errors that would even accumulate in time? Would add 1 gyro output as "null" 1 in every 20 samples work, or generate jitter?
With best regards, Mike
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