buggy tire temperatures?

@Nellix82 So for the question "why" you got the answer. The question "how can I tackle this" never was asked 😉

Is it only about heating up front tires or also about temperatures they're reaching in the end?

If it's only about heating up you can do something in you're out lap. Put the brake bias far to the front and then drive your out lap with the brakes applied. Keep the Brake temperature around 700-1000°, ideally in the 900s. You're tires will heat up . If you're fronts still take too long, weave a bit. Just look that you're not hindering someone else and set your brake bias back to the rear before you start you're flying lap.

If it's about peak temperature: raise the tire pressures. They will heat up more quickly and reach higher temperatures. You can also add some toe. That heats up the tires too. 
To avoid overheating the rears you can do the opposite: Reduce tire pressures (will add wear). But you can also change the driving a bit. Look for traction, avoid sliding. You can help that with other setup settings like adding more negative camber (to some degree until you'll experience the opposite), you can soften your suspension and rollbars, you can lower your rear ride height (as long as you don't start bottoming out).

You can also reduce rear toe which indeed does reduce heating up the rear tires, but it doesn't exactly help with traction and sliding. So you'll possibly end up with the opposite effect