JSTL: constant in an expression language.. is possible?

[sickness]

hello
I' using this expression language
<cut value="${sessionScope.pswRcv_user.desDomanda}"/>

that retrives "desDomanda" from "pswRcv_user" session Attribute.
It works fine.

I've done a class with some constants. This class (ProjectConstants)
contains
public String PSWRCV_USER = "pswRcv_user";

Now I want to associate the string "pswRcv_user" to the constant in the
jstl expression language.
Something like this:
<cut
value="${sessionScope.<%=ProjectConstants.PSWRCV_USER%>.desDomanda}"/>

but this doesn't work!
how can I do that?

thanks a lot guys
bye bye