The Cisco 887 supports Policy Based Routing (PBR) without a problem. I've implemented many installations with the 880 series routers and PBR, however combining two routers to make one big fat pipe is something I believe cannot be done alone as you'll need to request your ISP to aggregate the lines from their end as well.
Your best shot at the moment is to use PBR and send some traffic over one ADSL while the rest of the traffic traverses the second ADSL.
I'm planning on covering this scenario soon as it's a popular topic generally.
Please let us know if we can help any further.