can't access FreeBSD boot CD data (but can boot just fine) using IP KVM "fake" drives

[George Sanders]

Most modern IP KVMs allow you to specify a ISO image, and they will feed it to the computer via USB and allow you to boot arbitrary "cds".

However, I notice problems in both standard FreeBSD install discs and FreeBSD-based live CDs, wherein the CD will boot and run just fine, but when it comes time to read data off of the CD, the running system cannot access it.

So, for instance, I boot with my KVM attached and I see this in dmesg:

ums0: Startech.com server remote control 
device_attach: ums0 attach returned 6

and the system continues booting, but then:

[*] Extracting filesystems
/dist/mountcd: Can't open /dist/mountcd: No such file or directory
[*] Error Extracting Filesystems

(this was with ROFreeSBIE)

With the plain old FreeBSD disc 1, I can go all the way through the install, but I cannot choose "CD/DVD" as install media, I have to ue the FTP option ... somehow I can boot up and use the install CD, but I cannot read any data on it.

... so my question is:

What flags/options/whatever can I feed the booting CD, in the loader, to tell it "just keep using that same old USB CD"  ?

Thanks.