Use of cash in a simulation


I am building a strategy where I am buying certain type of stocks when they appear through the use of the "dynamic weight" tool with weekly reconstitution. Once bought I intend to keep the stock for a year.
A big chunk of the time, there is only partial positions or no positions. I would like the remaining cash to be invested in another strategy or an ETF such as SPY, until there is need for this cash to be invested in the strategy.
Is there a way to model it through simulated and live strategies?

I am using books to simulate different cash levels, just add the strategy and than the ETF... but it is not dynamic...

Thank you for the answer. i do not think that it does what I am trying to do which would be more dynamic.