Custom chart without using waveform module

I am trying to create a custom chart without using the waveform element.
How it works at the moment:
I run a python script on Raspberry Pi every minute using cron. It reads various sensors and changing switch and dimmer states and then it updates the Nextion 3.5" Enchanced display.
First page is showing sensor reading for all zones and is on for 99% of time. The following pages show detailed readings for each zone and a chart with history of readings for sensors in each zone.
I approached the chart plotting in the following way:
I have variable on page 0 that has a long string containing concatenated three digit readings that is updated every minute by PI. Once I change the screen I have a preinitialize event that draws lines for each reading. It works fine but the problem is I have several screens with many varibles per screen which means many 270 long stings - this quickly overflows the memory.
Is it possible to draw the charts on all pages on update without keeping the data stored as variables by sending line command with coordinates from PI over serial interface? Then I would like the chart to visible once I change the page without sending a call for data to PI.

If the chart is global, you should be able to query its values from any page on the Preinitilize Event tab.