If grilling outdoors, prepare coals. If grilling on the range-top, lightly oil the grid and heat just prior to preparing the tenderloins.
On a cutting board, place 4 slices of bacon lengthwise with edges overlapping, to make a rectangle. Repeat until you have 4 rectangles, one for each tenderloin.
Press a fresh sage leaf on each slice of bacon, then place the tenderloin atop the sage leaves. Season with freshly ground pepper, then carefully roll the tenderloins inside the bacon to achieve a cylindrical shape. Secure each with 3 or 4 lengths of kitchen twine and brush with canola oil.
Grill the tenderloins for about 4 minutes total for rare to medium-rare doneness, rolling them constantly with tongs so that they cook evenly.
When done, quickly clip away the twine and slice each tenderloin into medallions, ½–1 inch thick. Arrange the slices on the plate and top each with a large pat of butter.
Yields 4 servings, as a main course.