Just found an easy way on how to use gels without using gaffer tape or zip ties for my Profoto flashes. Also without getting in the way of any light modifiers.
Keep in mind if you use the modeling lamp on full power (300W) the temperature in front of the frosted glass of the Profoto D2 gets around 160°C and will deform the color gel a little bit. If you turn down the modeling light a tiny bit it should be perfectly fine.
I use standard Lee filters and they are meant to withstand temperatures up to 180°C. They also have HT filters that go up to 220°C in case you need it. I measured the temperature myself. Apropos the front metal ring of the Profoto D2 will heat up to around 70°C.
I used a 3d printed circle cutter to cut my gels to a size of exactly 90mm in diameter. You can download the circle cutter from here:
Press on the frosted glass and clamp the gel underneath the 3 spring-loaded clips. If you cut your gels to exactly 90mm in diameter they will fit perfectly and there is also enough space around the frosted glass for the ventilation. Btw. the frosted glass of the Profoto D2 has a diameter of 91mm.