Search two indexes at once.

Let me explain my situation.

I have a LOT of documents to index, and more are added each day.
Since indexing takes so long I have done this.

There is and FTP folder where documents are added every day, and indexed ay 8 AM and takes only a few minutes since it has only documents for the current week.
On friday all these documentas are moved to another folder where all docs are acumulated. This folder is indexed early Sunday morning and takes a long time to finish.

Obviusly I use two different indexes.

So now my search form has a radio button with two options: Search current week / search all previous documents.  According to this button I call one of the two indexes above.

My question: How could I call two indexes from one search form and have all the results show in the same page, one after the other?  That way I can get rid of the radio button.

PS: Al this will go away the day we have incremental indexing !!

Sincerely

Gastón Groisman