I assume you want to satisfy some requires from some other packages,
although you mentioned without rpm and/or creating one, here is how easy
it is to bypass using and satisfy whatever requirements that
other package has, assuming you really want to bypass the requirements,
here is a minimal spec file, say something like dummy.spec, build it as
root or non-root with the following stanza:

rpmbuild '_rpmdir /tmp' -bb dummy.spec

you should end up with something like:

Wrote: /

install it with (you may need to be root here though):

rpm -Uvh /

here is the sample spec file:

# spec file starts
Name: dummy
Version:1.0.0
Release:1.0.0
Vendor:dummy
Group:dummy
Summary: Provides %{name}
License:%{vendor}
# in Provides: you add whatever you want to fool the system
Provides:another-dummy >= 3.4.5-6.7.8
Provides:yet-another-dummy =< 3.4.5
Provides:also-dummy
Buildroot:%{_tmppath}/%{name}-%{version}-root

%description
%{summary}

%files
# spec file ends

I was wondering if it were possible to add an entry without an rpm, or
creating an rpm at all. I guess not.