Thanks for reminder that 3.2 had the bug of showing “print” in the Reflow Interface (It was not there in 3,1.2 and Its not there in current Pre-releases)
Unfortunately whilst SumatraPDF printing can scale, As Far As I Know, it is always exported as an even ratio (so even if objects are buggy and on screen seem squished, they often print as x = y dpi), so its not normally possible to alter the aspect unless the printer driver has such controls.
SumatraPDF printing will be creating an image only PDF, If I needed to modify one axis scale then I would be considering Batch Image apps such as IrfanView which can work with image PDF.
Before that I would be looking closer at why the problem is there in the first place. is it bad source content or is the ratio badly defined.