Read the content into a property, then split that property and get an item out of it. This of course requires that you know on beforehand that the file will have (at least) as many lines as you have properties.
<Target Name="ReadFile">
<ReadLinesFromFile File="$(MyInputFile)">
<Output TaskParameter="Lines" PropertyName="FileContents"/>
</ReadLinesFromFile>
</Target>
<Target Name="CreateProperties" DependsOnTargets="ReadFile">
<PropertyGroup>
<Line0>$([System.String]::Copy( $(FileContents) ).Split( ';' )[ 0 ])</Line0>
<Line1>$([System.String]::Copy( $(FileContents) ).Split( ';' )[ 1 ])</Line1>
</PropertyGroup>
</Target>