My advice is to just take the bond, and subsequently forget all about it!
A lot of guys have left prematurely (aka before the 5-year priod had ended) and no one was ever pulled into court over it.
Remember, you're dealing with the former USSR here: Their system was based on intimidation, hence airBaltic thinks they can scare people into staying.
Indeed, it's even rumoured that the Latvian Law prohibits bondings extending beyond 1 year, so they'll never be able to go to court over it. As with so much other stuff in Latvia, it's just a big act of bluff. If they were to end up in court over the matter and loose, it would create precedent...and it would be against the very fragile egos in the region to ever risk such a faceloss.
How can they bond you for linetraining, will it not be conducted as revenueflights or what?
Do minimum 1 year with them...and then tell them where to go, should they hit you with a claim!