Think about the other solution which is to use the rectangle marquee tool followed by the menu Image >> crop (instead of using the crop tool). You have the option to set the aspect ratio as you with. That selection is sticky and should remember the last used ratio.
The best solution by far in Elements is to use the 'Open in ACR' dialog, even for jpegs. The ACR version of Elements allows you to define a 'custom' aspect ratio which will be added in the default options in the crop menu. Click several seconds on the crop tool in the upper tool bar and choose 'custom'.
Beside being non destructive, the ACR crop can be applied easily to several files in the film strip when a batch of files are opened in the ACR at the same time.