FYI, I was able to find a solution to this issue. Instead of converting the ASCII string to a decimal byte-stream, you would instead convert it to a hex-string and use the following set command.
# set access address-assignment pool yourpool family inet dhcp-attributes option 43 hex-string <long_hex_string_without_0x>
(e.g. set access address-assignment pool yourpool family inet dhcp-attributes option 43 hex-string 31302e312e312e31)
Note: the hex-string 31302e312e312e31 converted back into ASCII would be 10.1.1.1 (just an example)
I also had to set option 3 for the gateway as the IP phone I was testing with would not get a gateway with "route" dhcp-attribute.
I hope this helps others.
-Chris