Oops!
Sorry! I must learn to read posts properly. I thought that you were trying to block a particular overseas number.
I've looked at the instruction manual to see if there's a + button (because you could replace the initial 00 with +, thus saving you a digit) but I can't see one.
When I've used the memory stores on phones, I've been able to store just the first part of a number and add the last few digits manually. e.g. I used to have to dial quite a few numbers that started with 01473693, with three extra numbers being added to the end for specific departments within the company. So I just programmed '01473693' into the phone and, when making a call, listened as my phone dialled from its memory. When it got to the end, I simply added the last three digits manually.
So perhaps you could do something similar? i.e. store the whole of the phone number except the final digit. When calling, listen to the tones. When they stop, just add on the final digit manually.