Split flows across Domains

Hi, Are there any ISPs that do, or desire, splitting traffic across different ASes for prefixes learnt via an exterior gateway protocol (say BGP)? For example, an ISP can learn two different equal cost routes to a foo.com server via two different autonomous domains. It can thus split different flows (based on src-dest IP, src-dest Port, TOS, etc) across these two paths. Do operators currently do this? Folks can send me replies offline in case this constitues a "trade secret"! Thanks, Glen