The key to jhana seems to be stability of attention. It isn't that you try to make the breath pleasant, so much as concentration itself is pleasant, and most people are watching the breath. If you have any pleasant sensation anywhere, you can simply watch that. If nothing seems pleasant, just watch anything at all - whatever captures your attention most easily.
My first forrays into jhana were accidental. I was a teenager, and I was trying to learn telekinesis (hehe). I was staring at a psi wheel for about 10 minutes, and I began to notice how incredibly beautiful it was. I looked around and everything was glowing vibrantly with color. I didn't know what it was at the time. Later on, when I started meditating, I liked to do body scanning - where I just placed attention on different body parts in sequence for a few seconds - and after a while each thing became very pleasant until the whole body was buzzing with pleasurable tingles. From there concentration is very easy, so you can just go along for the ride. It seems very easy just to stay with anything once you've stabilized the awareness.
So you can concentrate on anything at all, just remember it's the act of stabilizing your attention that makes the jhana, not any particular object or sensation.
A good way to think about it is trying to stop a train that's going down hill. The movement of attention has its own weight and momentum, so the first few minutes of applying the breaks might not make a noticable difference when you first start. Try not to think of it like you're vieing for control over your mind, but rather you're slowing it down with every moment of sustained awareness of a single thing. Every time you notice you aren't concentrating, just hold the attention on something. You will get carried off by the momentum again, but then you'll have a moment of clarity, and you use that to go directly back to the object. There's no reason to scold yourself or anything because that's just keeping your foot away from the brakes.
Lastly, if you find your clogged nose distracting, that means you're already focused on it, so why not just use that as your object of concentration.

Anything can become pleasant if you keep your mind open to the possibility.