Perhaps one could use the Saturn's RGB output and feed it into a scandoubler?
These devices will actually take a TV (15.75kHz) signal and "upsample" it to 31.5kHz so any VGA monitor (capable of a 60Hz refresh rate) can display that signal, and it will do so progressively rather than interlaced. Scandoublers were popular for a while during the Amiga's lifetime... I don't know whether they exist in some universal form (non-specific to the Amiga), though.
EDIT: when I said interlaced, that was of course referring to games using high-res modes, such as Radiant Silvergun. The more common low-res modes would already be progressive, only each line would be drawn twice in succession, therefore giving the "squareness" of the pixels more definition and making them look blockier. You know what I mean if you ever play low-res games on an emulator on the PC...