Is it possible to convert data from monthly frequency to annual frequency, but employing a weighted average rather than just a simple straight average of the twelve values? If not, is there some kind of workaround that is possible?

The root of my problem is that I need to calculate an annual average production rate from 12 monthly production rates. One cannot simply average the 12 monthly values, because each month has a different number of days and therefore needs to be weighted slightly differently to calculate the annual rate. I cannot seem to find a straight-forward way to do this with Eviews. As a workaround, I am currently creating a link from a monthly workfile page to a daily workfile page, then creating a link to an annual workfile page from the daily one. This gives me the correct data, but since I have several decades of data, the daily workfile page has a huge number of observations that inflates the size of my workfile and makes Eviews take a very long time opening and saving the workfile.

Any ideas?