Would the succession of Maria Teresa and her husband be a possible alternative? Maybe permanently giving up the Duchy of Parma (who would it go to, tough? Would it got to Napoleon II, if he survives?) , and having Lucca be integrated into Tuscany earlier?
Scraping the barrel, are you?
Carlo II di Borbone-Parma was somehow better than Ferdinando IV di Asburgo-Este, but that is a very easy result to achieve: on the plus side, he was a nicer guy and with some liberal (for a given value of liberal, at least); on the minus side, he never showed any interest in governing (in 1849, barely 50 years old, he abdicated, leaving the crown of Parma to his son Carlo III - a nasty man who got assassinated in 1855 by revolutionaries), liked travels and was a spendthrift and an hedonist and whenever he got involved in ruling his decisions were humeral and erratic. Incidentally, his marriage to Maria Teresa was far from a success story: the two were seldom together, their and it is surprising they managed to sire an heir. This said, I don't think it likely that either Carlo or Maria Teresa would have actually canvassed for the crown of Sardinia.
There would be also the problem of the succession of Parma: IMHO, the most obvious solution would have been to give Piacenza to Piedmont and Parma to Austria, but this would have given Austria a strong foothold on the right bank of the Po river and changed the balance in Italy.
There is also the question of who would support Carlo's candidacy to the crown of Sardinia, leaving aside the obvious problem of the Salic law. Louis Philipe of France might have supported him (Carlo II had recognized him as soon as he got the French throne), but Austria would have seen the danger of an increasing French influence in Piedmont-Sardinia, and would have been wary of the danger of installing a king with dangerous liberal leanings. I don't have any idea of what the UK would have thought of this possibility.
If this has to work (and it is a very unlikely possibility), the best option might have been for Carlo's son to get the Sardinian crown (he'd be 8 years old, which again would require a lengthy council of regency). Carlo jr. would also renounce his rights to the duchy of Parma, which at the death of Maria Louise would be split between Sardinia and Austria. Maybe Carlo II would also sell his rights in Lucca to Tuscany (as he did IOTL in 1847), and would have little or nothing to do with the education of his son. Maria Teresa would probably be on the council of regency for Carlo jr.
Carlo jr. was described by contemporaries as a "stubborn, impetuous child who never managed to grow up", and it is quite likely he will end up in the same way ITTL too: after all, IOTL he spent his youth in Piedmont too, enrolled in the Sardinian army by grant of his uncle Carlo Alberto, but not even the harsh army discipline succeeded in curbing his excesses; OTOH, he acquired a taste for everything military, although he never shone in the field. I cannot judge if living since boyhood in Turin under a Regency Council would have improved his character.