there are 2 ways to accomplish what you wanted:
1. you can populate the future input varaible values to the "base" value (e.g. 0). The forecasts should be the "base" forecasts. You can then test if the base forecasts are trending up or down
2. you can use UCM model (excluding ARIMA and ESM) and look at the OUTCOMPONENT dataset. Filter the OUTCOMPONENT dataset with _COMP_ = 'Filtered Level' and examine the _PREDICT_ column. This component is basically the "base foreccasts" without the influence of input variables.
thanks
Alex