Is there a phrase to use when someone is using a tool incorrectly so that to barely achieve the result?

Solution 1:

This is rare, and the wording isn't fixed, but I've heard in in real life, and there are hits on Google (without the quotes you get a lot more relevant hits, but they're buried in a lot of irrelevant material):

Hitting the nail with the handle (of the hammer).

Because it's an obvious metaphor (actually more often employed as a simile) you can get away with it not being well established. I've come across it in engineering (and science) circles in the UK, where tool metaphors are common, and problems in particular are often described in colourful terms.

It works well in a deliberately mixed metaphor: "Fred tended to use sledgehammers to crack nuts. Unfortunately for the rest of us, this time he decided to use the handle"