What you can do is adding a trace GUI element.
You have set FPS=100 and time step is 0.01 s
If you want to set ghost image every 0.1 s, then you should set the [u]Skip[/u] property to 9.
So that it only draw a marker every 10 input points.
You can set [u]Connected[/u] property to false so that no line are connected between markers.
You need to select one of the [u]Marker Shape[/u] and set a value for [u]Marker Size[/u].
[u]Marker Color[/u] is optional.
You need to enter variable/expression for [u]Input X[/u] and [u]Input Y[/u] so that EJS can draw it.
There are more optional property you can set up. Please check out http://www.um.es/fem/EjsWiki/Main/ElementsTrace for detail information about each property.