I have a single output variable $y$ and a number of inputs $x_1$, $x_2$, etc. These are time series. Each $x_i$ explains the changes in $y$ in specific circumstances, and the goal is to have a linear model that looks like $y=b_1x_1+b_2x_2+...$ The point is that each $x_i$ must be sampled on different criteria specific to its qualities, and its relationship to $y$ to be established only at those situations when that particular $x_i$ is the lead influence on $y$.
My approach is to take one sampling method $s_1$, sample $y$ and $x1$ on it, specific to $x_1$. Do the regression $y$ on $x_1$. Then, take the error $y-b_1x_1$, sample the error on another sampler $s2$, and regress this on $x_2$.
What's the name of this method, is there a regression of this sort? Does it sound like the right solution to my problem?
Due to practical constraints, I want my model to include all $x$s at the same time, rather than switch between different models on the fly.