The problem is how do we make migrating to such a scheme politically tenable? Right now we are in a situation where politicians dream up new "multiplier" laws (for instance, throwing on extra punishment or at least higher minimum punishments for committing a crime while wearing a mask) so that they can be seen as "tough on crime". We aren't just coasting in the wrong direction, we are making an effort to go in the wrong direction.
It seems hopeless to me. The general population doesn't give a shit, they are bloodthirsty and think of "criminals" as some distinct segment of society that they don't need to empathize with (hell, we can't even get executions widely abolished, a far more egregious issue...) So long as that is the case the politicians will keep on making the situation even worse for personal gain.
Under the U.S. sentencing guidelines (e.g. http://www.ussc.gov/Guidelines/2011_Guidelines/Manual_HTML/5... or state equivalents), this is already the case. Although you may be sentenced to "105 years" for multiple crimes, if they're related to the same activity, those sentences are usually served "concurrently." It's left to the judge's discretion.
Your complaint at this point should be with prosecutors that use the most draconian possible sentence to promote themselves and pressure defendants, and with a media that loves the shock value of numbers like "105 years" when such a sentence would almost certainly never happen.
Without the laws to enable it, the prosecutors would be unable to do that, and the only way to prevent prosecutors from doing that is to make laws that forbid it. The only way to change this while working within the system is through the legislators.
One way is to highlight cases with generally good people getting destroyed by overzealous prosecutors. Its unfortunate, but this is one of those issues where optics is huge. If you're black or hispanic or have tattoos, many people will assume "oh, well he probably committed another crime anyway, so its okay to go overboard on this one".
It seems hopeless to me. The general population doesn't give a shit, they are bloodthirsty and think of "criminals" as some distinct segment of society that they don't need to empathize with (hell, we can't even get executions widely abolished, a far more egregious issue...) So long as that is the case the politicians will keep on making the situation even worse for personal gain.