I have to admit, this is still one of the biggest annoyances of AP for me. I'm very used to using Photoshop's crop tool where I can enter the pixel dimensions into the crop tool, it will then maintain the aspect ratio and pixel sizes then resize to the specified pixel sizes when you apply the crop.
The workaround that I use for this situation, is setting the Custom Ratio of the crop tool to the pixel size of the image.
For example, I know I want a 2480x3270px image (scaling down from a 10000px+ TIFF file), rather than using Absolute Dimensions I use custom ratio set to 2480:3720.
This will lock the aspect ratio, allowing you to scale and reposition the crop tool as needed.
Apply the crop when happy and set the width/height to the document when exporting the image.
It's certainly not ideal, but it looks like the resampling still hasn't been included.
