Send Subcommands to iSeries FTP Server via PowerShell

I have a Script written in Rexx, that parse a text entry with the following format

Server:
user:
password:
DestPath:
SrcPath:
Command: (put | List | Get …)
Subcommand (Quote CRTPF | Quote Locsite | Rename …)

I want to re-write the same script using PowerShell (and parsing data from the same text file)
I’ve managed to establish connection with the server using FTPWebRequest, also to find the equivalent for each command, but I haven’t find a way to send the subcommands to the server (sometimes there is more than one subcommand)

This is an example of a subcommand that I want to send to the iSeries FTP Server :
QUOTE CRTPF FILE(Folder/Subfolder) RCDLEN(70) SIZE(*NOMAX)