Perch don't mind wire traces at all, they are that aggressive when striking at lures they don't notice. Besides in the UK you should never consider lure fishing without a trace, because even in waters that "don't" contain pike you will encounter one at some stage. If you don't use a trace you'll end up leaving a lure in a pike much to its detriment.
If your at all worried about the stiffnesss of a trace affecting the lure or the fish seeing it, just use one of the softer wires, like Drennans soft strand or the Fox soft strand. I have used both (more the drennan) for my ultralight and light lure work for the past 3 seasons and had no problems at all. Took 28 perch in a couple of hours from the local canal last week on 30lb braid and 28lb trace, none of them above 12 oz and they didn't seem to mind the trace.
I've gone a bit here haven't I, basically use a trace, you'll have no problems with the perch and best of all you might get the odd fry feeding pike this time of year as well.