I could put in series with a diseqc swich and make one receiver master (supplies power) and one receiver the slave (no power).
As the power from the powered output could reach the 'no power' output that way, I'm not sure if the 'no power' output transistor could get damaged. That is at your own risk.
I would say: NEVER use such a power pass both ports - both ways - splitter for combining two receivers.
For that, there are both ports power pass
one-way splitters, or ONE port power pass one way splitters, or even smart
priority switches (but these act more like switches than as splitters, it seems: the passive port shows random losses, when the other port has control).
The splitter you show is excellent for
parallel use of diseqc devices; e.g. to split signal between diseqc 1.2 and/or 1.0 and/or 1.1 devices.
BTW I'm not sure what happens with 22kHz control in a setup like you suggested.
Could it still be provided by the not-powering port, or can it only be provided by the powering port?
Or is it dependent on maybe various RF/HF filtering inside the splitter?
Never tested such a setup, though.
Greetz,
A33