Gil writes about a chiddush he came up with a while ago, then saw in a commentary on the Shuchan Arukh. I'm glad to hear it, because I always assumed that to be the case - we only say 'ki shem Hashem ekra' when there's no problem of 'Semikhat Ge'ula le-Tefilla'.
There are a few ramifications to this:
When it comes to Ma'ariv, the requirement of 'semichat ge'ula le-tefilla' is superseded by 'tefilla be-tzibbur'. Thus if one shows up to ma'ariv as the minyan is starting shemoneh esrei, he should start with them, and say the first part - Shema and its brachot - only afterwards. Since there's no 'ge'ulah le-tefilla' here, he should say 'ki shem' at maariv as well, no?
There are a few ohter scenarios like this (e.g., tefillat tashlumin) - would this be the proper course of action?
Truthfully, as Gil pointed out, this is a relatively late custom anyway and is not an integral part of tefilla. So if you don't say it at mincha even, no biggie. I just wanted to point out certain conceptual ramifications of a prevalent custom.