The problem you would have is getting effectively the sample start of sample A (let’s say OSC1) to trigger the restart of Sample B (OSC2) to force an oscillator style sync like would happen in a synth with hard sync. It would at least take a dedicated tool and as I’m not a developer I have no idea if it would even be possible. You’re better off using a VST with the feature as suggested, but I am more than happy to be proven wrong.
Since Renoise has samples, not really OSCs, it is difficult to implement a real OSC sync. I am not saying this is not possible, but it certainly would require a new concept for some kind of a special oscillator / single cycle / wavetable mode instead a resampler/player. So this would require a lot of effort and time, conceptual, programmatical and also design-wise, so I doubt that this will be a topic at all (since there are so many other more obvious points)
Much more easily to implement would be a ringmod cross-sample mode, or a sidechain for the ringmod device. Still even these simple solutions could not compete with a real osc-based/synthesizer-based conception, but would give interesting new sound possibilities at least.