Referencing `this` in a capture set

Imagine I want to perform an operation in 2 steps. I can easily do that by returning a boxed function:
```effekt
interface Foo {
def foo(): Unit => Unit at {}
}
```
but what if I want the second part to also be able to perform further effects that the handler has access to?
What I want is something like:
```effekt
interface Foo {
def foo(): Unit => Unit at {this}
}
```
but that doesn't seem to work.

I'm thinking this must be possible, right? [Scala has it](https://docs.scala-lang.org/scala3/reference/experimental/cc.html#a-larger-example).
I guess I can use CPS
```effekt
interface Foo {
def foo { block: { Unit => Unit } => Unit }: Unit
}
```
However, the CPS version is not as useful, since the second step cannot escape the block, so I can't store it in a list on the outside, for instance.