Topic: Trying to build nested RESTful route in code?

Everyone on this forum seems to be doing well with RESTful routes and I am enjoying them tremendously. I am attempting to use this approach in a very non-standard way. So here goes the foundation of my question.
In a nested RESTful route we call it something like this;
This is easy and it assumes that we are looking at ONE parent record to scope the children.

Now, what happens if there are a group of parents built into the instance variable of the controller?;
@parentscope = Parent.find([1, 2, 3])
We call the nested RESTful route like this;

Where I'm stumped is that I'm faced with the challlenge of building this multi-scoped nested RESTful route in code and delivering it to a 'link_to' statement.
I know you must be thinking, "how did she paint herself into such a corner". Currently, (thanks to Alex) I'm able to deliver this value as a field in a 'link_to' like this;
<%= link_to 'Place to go', eval(table.row.routepath) %>

My guess is that I must build a method in the parent model.rb to assemble this value, but I can find no examples of how this might be done.
I will pay money or work for slave wages in exchange for help on this.
Thank you,