Blue Guide on Scelex Dallara

I've some problems with the blue guide on my two Scalextric Dallara cars as it will not work together with my lap timing. I've modified a Ninco Spirit lap counter (I saw this on a Swedish web site) which uses NIR (Near IR) LEDs probably working at 850 nm. Through my work I've some experience that some seemingly opaque plastic materials transmit in the NIR. I did an experiment to test my theory and painted the guide blades with black Humbrol paint. It worked for about 20 laps on my track (36,3 m or 119 ft) then almost all of the paint was removed. It obviously works but it's not a permanent solution.

Does anyone have any good ideas? (Except changing the LEDs, which I don't especially fancy.)

Best regards,

Claes

PS. I'm using Lap Timer 2000 by Gregory Braun. It does the job, has nice features, looks quite nice, and it's free.