You can do it by offsetting the mesh temporarily, which will force DynaMesh to update:
[IButton,UpdateDynaMesh,"Update DynaMesh for current mesh",
//first record the current axis setting for Offset
[VarSet,tmpMod,[IModGet,Tool:Deformation:Offset]]
//one of the axes must be set, so set it to 1
[If,(#tmpMod != 1), //if it's not set to 1 (X axis)
[IModSet,Tool:Deformation:Offset,1]
]
//turn off the Dynamesh button
[ISet,Tool:Geometry:Dynamesh,0]
//offset the tool a little
[ISet,Tool:Deformation:Offset,1]
//undo the offset
[ISet,Tool:Deformation:Offset,-1]
//turn on the Dynamesh button - mesh will update
[ISet,Tool:Geometry:Dynamesh,1]
//reset the Offset axis setting
[IModSet,Tool:Deformation:Offset,#tmpMod]
]