You can  have flow dividers in SWMM 5 dynamic routing by using Storage Nodes for the dividers, OUTLET links for the downstream links and minimizing downstream HGL effects. The needed components are:

 1.   A Storage Node for the divider node as a OUTLET Link does not have a Surface Area,

2.   Two or More OUTLET Links as the downstream diversion and cutoff links,

3.   Two or More Rating Curves to divide the flow up based on either depth or head,

4.   Pumps, Outfalls or Steep Sloped Links Downstream of the diversion and cutoff links to minimize downstream HGL  effects