I would like to suggest that you can remove it and cut it to go back into your compost pile, but it's such as healthy and thriving plant that did well even without your care. Might be having awesome potatoes!

There are people that will tell you that you cannot grow plants in a compost pile and yet they will tell you to make a Lasagna planting bed which is really a compost pile. I have had many different plants germinate and grow in my compost piles over the years, although I have not really let them get fully mature there since the compost was taken out, spread around, and those plants transplanted to continue growth in the new bed. Often the fruits were very good although sometimes they were not. Go ahead and plant in that cold compost.

I think sedum might not give you much return for the cost of using them to make compost. The whole idea of compost is to recycle things from your home, yard and garden that you otherwise would have thrown away. Like fruit peels, lawn clippings, spoiled fruits and vegetables, etc. Those things are all considered green for your compost. Browns would be leaves, shredded newspaper or cardboard, and eggshells. Mix the greens and browns together and you have a garden amendment that cost you nothing and helps to keep landfills from being loaded up with things that are still useful. And these items are all free. I wouldn't buy seeds to plant something just to make compost out of it. You may be thinking of the principle of 'green manure' where the garden is sown with winter rye, red clover or hairy vetch, plants with short life span, that also fix nitrogen in the soil as they grow. They are planted in fall and the roots help to maintain the soil through winter and in Spring they are turned under to fertilize the soil for planting a garden. If you have a garden you don't need to grow anything green for the compost pile. As you trim and thin plants through Spring and Summer, put your trimmings in the compost pile. Add all of the grass clippings, junk mail, newspapers, cereal boxes, kitchen waste, leaves, stems, sawdust(from non-treated wood only), wood ashes, chicken poo, cow, horse, goat, sheep or rabbit manure. Things to avoid in your compost: grease, meat, pine, citrus, pet waste.

In order for a compost pile to work it must be aerated occasionally. Otherwise it will compact and stop working. Go ahead if you want to but you won't have a working compost pile. It would just be a raised bed