I like 'tackle it in a roundabout way.'
I'm not as convinced about 'ass-backwards,' because it means exactly the opposite of the right way, i.e., the wrong way, the cart before the horse. So you could use it in a negative sentence like 'Let's not go about this all ass-backwards,' but you wouldn't say, *'Maybe there's not a direct way, but is there an ass-backwards way?' Also, its register is obviously a lot more colloquial.
The old threads in the archive really aren't much help except for 'in a roundabout fashion' (and 'way' is better for that). For the record, pell-mell and circumstantial are both bad options. (Well, 'circumstantial' can mean 'umständlich,' but in practice it usually doesn't.)
Just for brainstorming, something sort of similar might work, e.g.,
You don't have to / Let's not ...
make things unnecessarily complicated
take the long way around
go out of your/our way
go round Robin Hood's barn [BE]
take the most roundabout way
wander up/down a blind alley
beat about the bush
reinvent the wheel
confuse the issue
come at it from an angle
come at it from the back door
take the most circuitous route
Or it might help to flip it:
Let's just keep it short and sweet
Let's get straight to the point
Or in certain contexts you might ask
Is there a straightforward/simple way to do it / an elegant solution, or do we just have to ...
cobble/patch it together?
I realize none of those are exactly the same. There's still something else in the back of my mind that I can't quite think of, maybe from math or programming, but 'brute force' isn't it.