When you have CaseType2 opened, you will also have pyWorkCover page available. You just need to call pxAddChildWork on that parent page. That should be ideal approach.
Let us know if you face any issues.
FYI : You can also use a combination of pxCreateTopCase and pxMove activities which will ideally create the CaseType2 case independently and then you can move it under CaseType1 parent. But i will suggest using first approach.
Ok, I tried what you suggested and I still have "CaseType2 is not a covered class" error.
What I do now: I'm in flow in CaseType2. In utility shape I call my custom activity that is in CaseType2 class. The custom activity calls pxAddChildWork on pyWorkCover step page. When I look at the clipboard right before the utility shape (that calls custom activity) there is pyWorkCover page.
Any idea why I see the error? Does it mean that for prpc CaseType2 is not child. When I look at CaseType1 pyDefault rule I see CaseType2 listed as a its subcase.