You can flash from the microSD card. You need to have the card formatted in FAT32. Take the RUU_signed.nbh file and rename it to TITAIMG.nbh, then place it in the root of the SD card. With that card in your phone, reset into the bootloader. If the card is set up right, it should read the image and then give you the option to flash it. I use this method for every custom ROM I flash, but I've always done the normal PC install on stock ROMs (although I'm now flashing on the TP instead of the Mogul).
EDIT: Here's a link with a slightly longer explanation for the SD card method:
http://forum.ppcgeeks.com/showpost.p...14&postcount=5