Workarund missing Union support in Kotlin - kotlin

Question

I wonder if there is any better solution to my Problem.
I have a Service1 that handles two different input types (A|B) using method overloading.
A Service2 should provide a method that accepts all input types of Service1 and does some work with the result, which I do not want to duplicate.
I came up with two solutions, but neither of those is convincing to me.
data class A(...)
data class B(...)
class C
class Service1 {
fun doSomething(input: A): C {}
fun doSomething(input: B): C {}
}
// Solution 1
class Service2_v1 {
private val service: Service1
fun <T>doThings(input: T) {
val result = when(input) {
is A -> service.doSomething(input)
is B -> service.doSomething(input)
else -> throw IllegalArgumentException()
}
...work with result
}
}
// Solution2
class Service2_v2 {
private val service: Service1
fun doThings(input: A) = handleResult(service.doSomething(input))
fun doThings(input: B) = handleResult(service.doSomething(input))
private fun handleResult(result: C) {
...work with result
}
}
Since this only needs to work with Types that are known at compile type, I wonder if there is a cleaner solution with generics, similar to this pseudo code:
class Service2_notWorking {
private val service: Service1
fun <T : ArgumentTypeOf<Service1.doSometing>>doThings(input: T) {
val result = service.doSomething(input)
...work with result
}
}