Before I forget, thank you everyone for your comments and advice, much appriciated!!
The AS prepend option seems to be the best. At present it's this (And I was wrong, it was 8 prepends):
route-map Choice1-out permit 10
match ip address NOC-Prepend
set as-path prepend 7321 7321 7321 7321 7321 7321 7321 7321
So I'll bump it up to 15 and see what happens. MED seems to be out of the question, as I was told by two of the three carriers in question that they may accept the MED attribute, and the third didn't even know what I was talking about, so I left it alone. It would seem that MED, although great in theory, is one of those options that is not practical in production use for manageability reasons.
I'm working on getting access from my disaster recovery carrier to see how many AS Hops they see to my main site. I don't get the full BGP route table there, I only advertise, so I can't look there.
**Update. I'm only allowed to do 10 AS prepends, then I error out. Restriction of the hardware or IOS?
For reference:
Cisco Internetwork Operating System Software
IOS (tm) 3600 Software (C3640-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)
Technical Support: »
www.cisco.com/techsupportCopyright (c) 1986-2005 by cisco Systems, Inc.
Compiled Thu 24-Feb-05 15:52 by kellmill
Image text-base: 0x60008930, data-base: 0x60A3E000
ROM: System Bootstrap, Version 11.1(20)AA2, EARLY DEPLOYMENT RELEASE SOFTWARE (fc1)
ROM: 3600 Software (C3640-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)
XXXXXXX uptime is 8 weeks, 4 days, 22 hours, 20 minutes
System returned to ROM by reload at 17:38:43 EST Fri Mar 5 1993
System image file is "flash:c3640-i-mz.122-28.bin"
cisco 3640 (R4700) processor (revision 0x00) with 98304K/32768K bytes of memory.
Processor board ID 27581893
R4700 CPU at 100Mhz, Implementation 33, Rev 1.0
Bridging software.
X.25 software, Version 3.0.0.
2 Ethernet/IEEE 802.3 interface(s)
2 FastEthernet/IEEE 802.3 interface(s)
DRAM configuration is 64 bits wide with parity enabled.
125K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read/Write)
Configuration register is 0x2102