Moving text to specified position using xsl

I apologize if this has been asked before, but I don't even know what terms to search for. I'm a beginner with xml and xslt and am looking to create html output from a xml file. My problem looks like this:

My text is:

This is some text. This is the last bit of text.
This is some other text.

The output I want is

This is some text. This is some other Text. This is the last bit of text.

I cannot just tag

<a>This is some text.</a> <b>This is the last bit of text.</b>
<c>This is some other text.</c>.

What I want to do is place a marker for where the text needs to be inserted. Sort of like this:

This is some text. <insert n="1"/> This is the last bit of text.
<addition n="1">This is some other Text.</addition>

The added text can be anywhere in the document, but it I can easily assign the n manually. Any ideas how to achieve this with my xslt stylesheet?

Many thanks!

Marie