it would be difficult to do, as the slideshow is set to 100% = full width in the style sheet of the ‘Slickr Flickr Galleria’;
even setting asmaller width and adding a float did not work.
the other reason is that with the largest images, there would only be a narrow strip on the side anyway. and the image widths vary a lot.
my only suggestion:
if you add a background image such as the ripped paper grey ones of the site behind the slideahow, the white space would be gone and look less ’empty’
it might work if you add a style such as the following to style.css of your theme (you would need to create the ‘slide_bg.png’ image):
.slickr-flickr-slideshow { background:#ccc url(images/slide_bg.png) left top no-repeat;}
.slickr-flickr-slideshow div { top:20px!important;left:20px!important;}
the second line is to move the slides away from the top left corner to show the background edge.
(untested)