Multiple Pair Shortest Path algorithm with Pregel

I have an application where I'd like to retrieve shortest paths for multiple source-target pairs. I'd like to write my own function but as far as I figured out that with Pregel, writing such a function is not possible. Because pregel allows sending only one double value to other nodes and in this scenario it is not enough. I'm wondering if I'm right about this or is there any way to write a Pregel Algorithm to work out this problem.

For now, I'm going with Core Graph Api. It's possible to do this with that and it's not that complicated.