How to set part of animation to play at different speed?

Hello. I have this problem. I have a character that runs by itself (not by user input) and has animation for that, then he must jump forward (also automatic) and then he falls down (no user input here either). Everything works just fine, but the 'obstacle' varies in sizes so sometimes i need to stay longer in the air to complete the jump. I tried manipulating animation speed, but it turned out that slowing down running and falling down does not look good. All this animation is called only once (so i have difficulties implementing three animations for each action). My question: Is it possible to change animation speed of part of this animation? For example i can split animation to clips by code, change speed for one of those clips, join 'em all up and run that then? Maybe someone have run into similar problems. Thanks in advance.