It is possible to update older VP2 without Bootloader (pre FW 1.9) to FW 1.9 with an Atmel AVR programmer.
I did the same thing with my VP2 Cabled FW Nov. 2004.
Steps are:
-Install Atmel Studio 7
-Connect the Atmel AVR programmer to your station board (Pinout see:
Building a Davis Vantage Pro 2 Updater - 6311VP2) i used an atmel ice 3, but a cheap USBASP AVR should also work.
-Select "Device programming" via toolbar and "erase chip" to get rid of protection fuses
-Readout eeprom, just to keep it safe, some calibartion settings for your station are stored here, but should not be erased after an update
-Flash the new software "Flash19.bin"
This should also include the bootloader, so you can update to 3.8.
Firmware Files:
Google Drive