Hello ScandinavianDude.....Welcome along.
Just a few points which may be worth considering...... depending on your temple -density [the density you are looking to achieve] and if you only need two relatively small ` bits` of lace/hair, John might just be able to order a square bit of lace equal to the amount of material normally used in a topper-system with a uniform density throughout...you could then just cut out sections to fit the areas needing coverage......there`s no point ordering a normal topper in your case as it`s curved /oval shaped and has varying densities .....you only need two small bits so I can`t see why it wouldn`t be possible to order such a thing...... you could then just trim/cut off several ` bits` as you need them.... obviously the density would have to be pretty ` light` to match your own hair in that area.....also, just order short hair..no point in getting the standard [default] hair-length of 6 inches!!
I sent an old system to a guy in Europe a while back as he only wanted to cover a pretty small area on which he had visible scars where the hair wouldn`t grow...he trimmed out some pieces but he found it wasn`t possible /practical as they wouldn`t stay on ....I don`t know what size he wanted to cover but probably smaller than what yours sounds like .....I guess, several layers of glue might be needed just to make sure they`d stay in place.... and as Baldrich said, you could get it ventilated [the direction in which they tie the hair in onto the lace at the factory] into a brushed-back style.
It sounds do-able ..you`d also have to specify single -tied knots as double-tied knots might lead to ` visibility` in that particular area, as the hair would be light-density and the casual observer would be able to see through the hair to the underlying skin ....usually they do an ok job in bleaching the knots, but sometimes it can be an issue ..can look like black ` dots` if they tie the individual hairs in with two knots..... the trade-off with single knots, is they can become undone and hair sheds out early...this can be overcome by applying knot-sealer to the underside of the lace ..it`s a liquid acrylic which dries to form a ` skin` and seals the knots, preventing them from untying....
I know you have a lot to consider before deciding what to do, but hope those suggestions may help you in your decision/s.