Powerstrip has a very frustrating non-intuitive interface. The easiest way to do this is probably to actually add a new custom resolution which is almost-but-not-quite 2048x1536. 2048x1538 should be good.
As you may have noticed, in the timings adjustment window you can only modify timings for the current resolution. You're locked out of making any changes that change the resolution, so in particular toggling "interlace" mode keeps the same resolution while halving the pixel clock etc.
This is a problem if your monitor can't display the "standard" 2048x1536@60hz timings, because you won't be able to adjust the settings downward to something the monitor can display. The only way you can do it is starts off in the custom resolution with custom timings from the start.
To do this, go to the timings adjustment window (at any resolution), and then click on the "custom resolutions" button to get to the custom resolutions window. There, use the "paste" button to paste from these Linux modeline timings:
ModeLine "2048x1536" 193.40 2048 2144 2624 2816 1536 1540 1565 1617 interlace +hsync +vsync
Why Linux modeline timings? Because it's been a really long time since I've done this in Windows and all of my custom timing stuff lately has been with Linux. These super-high resolutions aren't really very usable in Windows anyway.
Anyway, the next step is that you'll need to transform these timings into 2048x1538 resolution. Do this by toggling on the "Lock Geometry" checkbox. This locks things down so that the hsync, vsync, and pixel clock rates stay constant. The only things you change are the size and position of the actual used screen pixels within those timings. Why this isn't the default behavior I will never know--the bizarro default behavior is completely and totally unusable for any purpose whatsoever.
After toggling "Lock Geometry" on, change the resolution upward from 1536 to 1538. This will automatically adjust the other parameters as necessary.
Next, click on the button to add this resolution to the registry. It will tell you that you'll need to reboot for the change to take effect. Go ahead and close everything and then reboot.
After you reboot, you should be able to try out your new custom 2048x1538 resolution simply by selecting it in the normal way via the Desktop properties. You do NOT need to run Powerstrip to get custom timings to override the default timings--there are no default timings for the 2048x1538 resolution so the custom timings you manually created are the only ones in the registry.
If you try to do all this with the 2048x1536 resolution, then you'll have some frustrating undesirable side effects. The default progressive timings will be used until Powerstrip runs and overrides them. This is a big problem if you have a login screen, because Powerstrip won't run until AFTER you log in!