Found this through google and it worked!
However, some things needs to be pointed out:
Usb pendrives is a no-go - you really DO need a usb floppy drive. After trying and trying, I realized a 1,44MB floppy is needed. 720k is a no-go. Fortunately cutting a hole in one of the two 720k's I had available let me format it to 1,44MB.
My success was also limited in the first place because it had a single Kingston 1GB DDR400 stick. After changing dipswitch 1 and 2 to on, nothing happened. Looking in my old spares, I found a noname 256MB DDR333 stick which made it beep at last.
Using the solution provided by Tony then worked. Afterwards I could reinsert the 1GB module.
So an added list of things needed:
USB Floppy drive
1.44MB Floppy disk, not 720k
maximum 256MB DDR333 module(s)