I don't know that you can since each of PP's buttons is within a form
element e.g.
<form action="
https://www.paypal.com/cgi-bin/webscr" target="paypal"
method="post" name="modem">
<input type="hidden" name="bn" value="AMPPFPWZ.301">
<input type="hidden" name="cmd" value="_cart">
<input type="hidden" name="add" value="1">
<input type="hidden" name="business" value="" >
<input type="hidden" name="item_name" value="">
<input type="hidden" name="item_number" value="">
<input type="hidden" name="amount" value="10">
<input type="hidden" name="currency_code" value="AUD">
<input type="hidden" name="no_shipping" value="0">
<input type="hidden" name="undefined_quantity" value="1">
<input type="hidden" name="return" value="">
<input type="hidden" name="cancel_return" value="">
<p align="center">
<input type="image" src="
http://images.paypal.com/images/x-click-but22.gif"
border="0" name="submit">
</p>
</form>
and I don't know how to make a text link act like a form button - I expect
it can be done, I just don't know how.
Have you seen the PayPal site to see if they make a suggestion in that
regard?