In PHP is it possible to use a function inside a variable

I know in php you can embed variables inside variables, like:

<? $var1 = "I\'m including {$var2} in this variable.."; ?>

But I was wondering how, and if it was possible to include a function inside a variable. I know I could just write:

<?php
$var1 = "I\'m including ";
$var1 .= somefunc();
$var1 = " in this variable..";
?>

But what if I have a long variable for output, and I don't want to do this every time, or I want to use multiple functions:

<?php
$var1 = <<<EOF
    <html lang="en">
        <head>
            <title>AAAHHHHH</title>
            <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
        </head>
        <body>
            There is <b>alot</b> of text and html here... but I want some <i>functions</i>!
            -somefunc() doesn't work
            -{somefunc()} doesn't work
            -$somefunc() and {$somefunc()} doesn't work of course because a function needs to be a string
            -more non-working: ${somefunc()}
        </body>
    </html>
EOF;
?>

Or I want dynamic changes in that load of code:

<?
function somefunc($stuff) {
    $output = "my bold text <b>{$stuff}</b>.";
    return $output;
}

$var1 = <<<EOF
    <html lang="en">
        <head>
            <title>AAAHHHHH</title>
            <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
        </head>
        <body>
            somefunc("is awesome!") 
            somefunc("is actually not so awesome..") 
            because somefunc("won\'t work due to my problem.")
        </body>
    </html>
EOF;
?>

Well?