Hmm.... The only way I know is to replace all of the trash can icons in your current icon theme with the icons you want.
First, open Files as administrator (type sudo "your file manager name here" in Terminal) and navigate to /usr/share/icons. You will see all of your icon themes there.
Then, open the icon theme whose trash icons you want to change. Search for "trash". You will see all of the trash icons, in all sizes. Delete all of them.
Next, open the icon theme with the desired trash icons. You may see the folder that has the size of icons, like "16x16", "48"; or the categories, such as "places". Usually the trash can icons are in the "places" folder, and available with most sizes.
Finally, search for "trash" at each "size" folder, then copy the trash icons found to the same places at the original icon theme. This is the "tiresome" step I said, because it takes a lot of time to do this. You may want to open two Files application side by side for easier copying of icons.
See here for an example: http://www.flickr.com/photos/80519574@N07/7697336716/