You said you have four poles, so use them the best you can. Since you're limited, only jump courses of verticles. So instead of an X, do a low verticle. If you want to jump X's, do them one at a time.
Set up 4 jumps: one outside line, one outside single, and one diagonal. You can actually do a lot with this. Rollbacks, broken lines, jumps from both directions... you can actually make a pretty good course. I came up with one for you already. You don't have to use it, but it'll give you an idea of what I mean:
Sorry if it's a little hard to understand, I just put it together quickly on Paint. So basically the arrows describe which way you approach the jump and the numbers tell the order. 4 to 5 is a broken line, and 6 is a figure 8/rollback (you may need to trot into it if your horse does not know flying changes and you are worried about his balance).
Wow, I really like emeraldstar642's course, I may just try it sometime!
Here is another four jump mini course I like to do a lot. All the jumps are vertices, because you only have four poles. It's shaped like the letter 'Y'.
It's hard for me to explain the course, so here's a picture: