The only way I can see to do that is to have some intermediate pages which are not shown. Bear with me while I explain.

There are different page types in Gamebook mode. You can see this under the "Page type" dropdown for a page. The normal page type is "Text". This page only has text. There are also two others of interest: "Script" and "Script + Text". The latter will run a script and then dump out the text like a normal page. The former is a page that only has a script to run. What use is this? Well, it can be used to do some scripty things and then move you off to another page. It's just a transition page with no text of its own.
So, as somewhat painful as it might seem, create three intermediate pages (e.g. Page1_1, Page1_2 and Page1_3). For each, set the type to "Script". Then add script to set the variables you want (or whatever else). Be sure the last script command on each page is a "Move player to page" command, with page being your Page 2. The script will be run, and the player will then be taken to Page 2.
Note that I haven't tried the above, but looking at the Quest core, it looks like this is the way to do it. If that doesn't work, we'll try again.