I don't think it's as black and white as you say. What can we gather from the context? Let's look at it:
Acts 2:37-41, 44
37Now when they heard
this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men
and brethren, what shall we do?
38Then Peter said unto them,
Repent, and
be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
39For the promise is unto you, and to your children, and to all that are afar off,
even as many as the Lord our God shall call.
40And with many other words did he testify and exhort, saying, Save yourselves from this untoward generation.
41Then they that gladly received his word were baptized: and the same day there were added
unto them about three thousand souls.
44And all that
believed were together, and had all things common;
While you are correct that the audience he was addressing were Jewish people, whether proselytes or ethnic Jews. The things Peter tells them to do are actually repeated elsewhere for Gentiles.
So what did he tell them to do?
1. Repent (2 Corinthians 7:10)
2. Be baptized (1 Corinthians 1:14-17)
3. They believed (1 Corinthians 15:1-4)
So what I'm getting at is that the message surrounding Acts 2:38 not only applies to Jews, but to Gentiles as well. I just showed you the evidence.
I do not think it is necessary to attempt to separate this message from the context of the New Testament message to Gentiles. Why are you doing this?