Following the methodology described here, the WFC3 team has written a function to remove time-variable background from IR images and improve the ramp fitting.
https://github.com/shannnnnyyy/wfc3tools/blob/ir_tools/wfc3tools/wfc3ir_tools.py

The procedure will partially process a RAW exposure through calwf3 (with CRCORR=OMIT), remove the median signal per read from the IMA, and then resume calwf3 on the corrected IMA file, this time with CRCORR=PERFORM, in order to produce an improved FLT image.

The problem is that calwf3 fails the last step when the file is not part of an association. (eg. ASN_ID=NONE). This appears to be a bug in calwf3, which hopefully could be a simple fix?? We need this in order to run our pipeline to generate sky flats using exposures impacted by non-linear background. Tagging individuals involved in this effort @shannnnnyyy @heatherkurtz