From Tom Singer and MLB.com, via Pirates Prospects. Singer says indications are that Liriano will report on a non-roster invitation. Presumably, the contract would call for him to get something approaching his original deal once he makes the team. It would also save the Pirates an immediate roster move, so they can continue to cling to Jeanmar Gomez for a while.
UPDATE by Charlie: WTM, Vlad and I were all working on posts about this at the same time. WTM won! My take is here; Vlad's is here. I would add the following. This is the seventh paragraph of a Tom Singer article, so make of that what you will. If this is actual news, Singer buried the lede big-time. There's probably cause to treat this with a little skepticism until it actually happens (particularly given that we've already heard about two major-league deals for Liriano that haven't gone through). If it does, though, it might be an indication that Liriano's injury is more serious than we thought.
If the report is correct, that would represent quite a fall for Liriano, who was looking at a two-year guaranteed ML deal before suffering his broken humerus. Unless the contract has some unusual language, it's likely that his ML salary won't be fully guaranteed until he's added to the 40-man roster. He presumably will have an out clause to protect him from roster chicanery by the Pirates' front office - I'm not suggesting any ill intent on their part, but an ounce of prevention is worth a pound of cure.
Waiting until the end of spring training (or even the early days of the regular season) to add Liriano to the 40-man roster would be advantageous to the front office from the standpoint of roster management. It's often easier to slip semi-interesting players through waivers at that point in the season, since all the other teams are trying to do that same thing. Delaying the decision could make it easier to keep a player on the fringes of the roster, like Chase d'Arnaud or Jeanmar Gomez, in the organization as additional depth.
A minor league deal would also mean that Liriano won't accrue any service time until he's ready to be added to the roster. That shouldn't matter much to the front office, but it's potentially a very big deal for Liriano, as it could affect the ultimate size of his pension if he ends up falling short of ten years' worth of service time for his career. He certainly won't be lacking incentives to work hard on his rehab.