Spill Over type Load Balancing

Hello,

In cases of multiple asymmetric ISP services, the various types of load balancing examples on the Wiki really dont seem to apply since none of them are sensitive to the speed of the upload and download of each WAN.

If WAN1 is a 50Mb upload/4Mb download Cable Modem and WAN2 is a 20MB Download/1MB Upload DSL, then is it possible to create a watermark/threshold value that changes routing for the next sessions?

For example, if WAN1 has 3.5Mb of its 4Mb being used in upload, all new outbound sessions should “spill over” to WAN2.

Once WAN1’s upload drops below 3.5Mb, all new outbound sessions should “spill back” to WAN1.

Is this possible with Mikrotik?