Hi,
Yes they can, as long as they're going to cast it via bestow. The latest update to the Comp Rules makes this clearer:
601.3b If an effect allows a player to cast a spell with certain characteristics as though it had flash, that player may consider any choices to be made during that spell’s proposal that may cause it to have those characteristics. If any such choices could cause it to match these characteristics, that player may begin to cast that spell.
Example: An effect says that you may cast Aura spells as though they had flash, and you have a creature card with bestow in your hand. Because choosing the bestow ability’s alternative cost causes that spell to become an Aura spell, you may legally begin to cast that spell as though it had flash.
Nathan Long
Magic Rules NetRep