TV3 will, I imagine, be chagrined that he's not doing it for them. The truth, though, is that you really need adequate resources to do a show like this properly. A considerable amount of cash has clearly been thrown at transforming Rosenstock into his targets and most of the time it's money well spent.
Not all of it works, of course; then again, since when have sketch shows, even great ones like Big Train and Not the Nine O'Clock News, been anything but patchy affairs?
A werewolf-like James Reilly extolling the benefits of a good walk (to his local chipper) was a long stroll towards a predictable punchline, while a sketch featuring a coquettish Miriam O'Callaghan, head tilted, eyelashes fluttering like butterflies, using her womanly wiles to seduce answers from a shifty politician felt obvious and well-worn.
But when Rosenstock and his co-writer Ian Dempsey -- a frequently underrated creative partner in Gift Grub -- cut loose and let their imaginations run wild, the results were frequently hilarious.
Louis Walsh's History of the World, with the X Factor judge holding forth on the merits of Stalin, was pure brilliance: "His left arm, it was withered away. It just adds to the story. He reminded me of the young Tom Selleck. Okay, the critics say people got hurt -- it's a tough business! But everybody loves a bad boy. Look at Frankie Cocozza."
An MTV Cribs skit on Michael Flatley ("Check it out: this is where I keep me leprechaun homies"), who has Sally O'Brien of Harp lager ad fame on tap and keeps comedian Sil Fox stored behind his bookcase, was inspired lunacy.
In what's sure to be a recurring sketch, TDs Mick Wallace and Luke 'Ming' Flanagan are recast as DJs, a kind of Leinster House version of Smashy and Nicey: "Coming up, George Hook discusses intimacy issues."
Even when the show threatened to fall back on familiar material -- Vincent Browne grilling Joan Burton ("What's the point of Europe at all?") -- Rosenstock pulled a surprise out of the bag by having superstar DJ David Guetta invade the studio.
For a mimic like Rosenstock, an obvious pitfall is thinking that impersonations alone are enough to entertain an audience. Luckily, he and Dempsey recognise the need to have decent scripts to put in the characters' mouths. It's telling that one of the sharpest items on the show wasn't a bit of celebrity-slagging silliness, but a spoof reality show called Eviction. In all, a very bright start.
Meanwhile, down in the dimly-lit basement where RTE keeps the rubbish it should have thrown out ages ago, The Republic of Telly continues to fester and stink, and the odour gets fouler by the week.
I don't know which is worse: the gutless, toothless attempts to be a TV Burp for an undiscriminating studio audience who'd guffaw at a piece of faeces on a stick, the toxic glow of smugness that comes from those godawful "behind the scenes" interludes, or the continuing delusion that Jennifer Maguire is some kind of comedian.
This week they despatched the most annoying creature on the box since Bosco to the New York Comic-Con, where she insulted a variety of baffled Americans and rubbed a little smut into their faces.
In the face of this wretched puerility, someone dressed as a comic book superhero seemed like the most reasonable person in the room.
The Mario Rosenstock Show 3/5
The Republic of Telly 1/5