Show their current selected combination in the center with variations, each a variation on ONE parameter, arranged around:
When they click on one of the variations, it moves to the center, and new variants are created. You'd be crazy not to show the user preview of the choice they are currently interested in, and the images that show what varying a parameter 'mean' should be made relevant to them by showing variants on their current choice.
The idea is borrowed/stolen from Photoshop's variation tool for colour balance fine tuning - an excellent interface pattern for fine tuning multiple parameters where a preview is useful.
Some creativity is called for in adapting it. The arrangement shown gives you variation, plus and minus, on three parameters. Adobe have extended it to 12 parameters by the highlights/midtones/shadows/saturation choice. As an indication of one way to adapt that idea, we could have choices that allow LRUD (Left/Right/Up/Down) to all vary together, LR or UD to vary together, or one of L,R,U or D to vary - catering to even the most eccentric designs.
The variation is for 'border control'. I wouldn't attempt to show variation in the 458px x 25px part of the sizing using this layout. For reasonable sizes of borders this allows us to keep the image for each variation a fixed size. Additionally, if only part of the border box is being varied, say parameters affecting the top left corner, we only need to show that part in the preview images.