If anyone is insterested in the answer to the question, I solved the problem by remastering the distro, some days ago.
And modified it in the way that now it accepts the option
tce=[t]ftp://SERVER_IP/TCEDIR_PATH.
I reprogrammed too, the way it takes to load the applications on the X server. In order to accpet a config file outside the gz core image, and now inside the tce dir (wherever it's located). Got that folowing the syntax bellow:
[CONFIGFILE.CONF]
startuplist="applicationa, applicationb, applicationc"
keepuplist="applicationc"
applicationa_conf="-v -D -x"
applicationc_conf="-p /path"
In that way, I could load up the sound drivers, start them, start the X server and the rdesktop client. Passing all needed configurations, including the ip of the W terminal server machine where the clients is supposed to connect to. And if the ip has changed, I can just modify the rdesktop_conf parameters inside de config file in the tcedir indicating the new ip, without any needing to remaster the distro.
So, I reached my objective of getting W terminal server clients served through network boot. With the machines starting without any hard disk and getting inside the W login screen just after the boot.
Amazing fast.
Any details, post or send a pm. It'll be a pleasure if this solution could help anybody else.
Thumbs up to TinyCore!
PS.: the option keepuplist inside the config file is used to keep some applications up running and/or the user inside some of them, when it's closed by the standard ways.