This is possible, if the phone is rooted. And I suppose it might even be worth doing if you can get an old G1 off craebayslist, but probably not with the device that is your "phone".
Normally when you connect your android device to a computer (or the TV) and enable mounting, it mounts the SDHC card or non-removable equivelent. But that's not the only possibility. With some root level reconfiguration (replacing vold) the usb storage driver on the phone can actually be pointed at anything that looks sufficiently like a disk - ie, a physical disk, or a file containing a disk image.
Since there are also ways to get the linux underlying a (rooted) android device to mount a filesystem served over the network from your pc, you could now point the usb storage driver at a file on your pc containing a disk image of a FAT filesystem containing the media you want to serve.
(There are some potential shortcuts to merge the steps, but it will be easier to get the PC-to-android and android-to-tv parts working separately first)
You would still have to create disk image files on your pc much like you now copy things to usb sticks, but you could automate that and only eat up hard dive space having duplicate copies in the images, and you wouldn't have to physically move the USB stick.