A table that adopts the rule that all dice rolls are open is almost certainly of the view that fudging dice rolls is not acceptable behaviour.
If this rule is imposed by the GM (you) and yet they still want to fudge - why have they hamstrung themselves?
If the rule is a consensus of all the players at the table then it is poor form for the GM to unilaterally override the way all the other players want to play. In this case the best option is to talk to the players (this may have been mentioned before on this site) and get their buy in for what you are trying to accomplish.
By the way, we don't really know what you are trying to accomplish and perhaps you should ask that question.
All you say is "the planned story leads to an other direction than the dice want" which sounds like the really, really bad kind of railroading. If the story really has to go in a particular direction (and there's nothing wrong with that) then this should not be something that is left to chance (or player choice). If it needs to happen, it just happens: move along, nothing to see here.
Alternatively, if you are trying to save the players from the consequences of actions - don't do that. Players play games because they want their choices to matter. Taking calculated risks and heroically overcoming obstacles is way less fun when you only do it because the GM lets you win: assuming your players are older than 12. Failing is fun too, especially failing heroically.
Some groups have a problem with player death. If that's what is concerning you then change the rules so death is not a possible outcome. Given that my first ever PC died in the third room of his first dungeon (death by stirge) this has never been a problem for me.
Notwithstanding, here are some techniques:
- Player call: "If I let this roll stand you're probably going to die: are you ok with that or do you want me to fudge it?"
- This is not the roll you're looking for: "A 20. Well, that's a miss, you can go about your business, move along."
- Reasons: "Well that would have been a hit, except he's fighting uphill into the sun which gives a one time circumstance modifier of -6. Oh, and he's suffering from ... scurvy, yeah, scurvy which comes and goes but this round gives -10 so that 19 just misses."
- Idiot DM: "An 8, silly me, I should have rolled a d6 ... a 2.
- Just enough: "How many hp do you have? 7? It does 6."
You may object that all of these will be known to the players. Well, here's a little hint: don't assume your players are brain dead morons. If you fudge, no matter how you fudge, your players will work out you are doing it. Far better to be upfront about it and maintain the bonds of trust.