How to choose a tempo for a song using metronome [Resolved - with a really good idea!]

On my Roland MC50 I can set the metronome to sound when recording, playing, or stopped.
In Stopped mode, the metronome sounds all the time and I can sing and turn the dial until I think the tempo is right.
 
In Sonar I can only set the metronome to sound in record or play mode. There is no "Stopped" setting.
 
In Play mode it only uses the start tempo. If I change tempo after I click Play, the tempo does not change.
(note: I have not recorded anything yet. All tracks are empty.)
 
I found a tap-tempo button in Project > Insert Tempo Change, but you cannot hear the metronome
there and I cannot sing against anything to see if it's right. All it shows is the tempo number.
 
I am using my hardware metronome now, but does Sonar have a better way?

I mapped the Project -> Insert Tempo Change to my Alt-T key. Then when I need to set a tempo for a new song, I press Alt-T and click on the Tap button while singing the song. When I'm satisfied with the tempo, I click the OK button on the tempo popup and the tempo is set.
If I want to check the tempo with the click, I click on the Metronome During Playback and play a few bars before recording. No need to enter any numbers. I just go with what feels right for the song.
I use the same process if I want to change the tempo during the song. For anything more complex, I go into the tempo map and make my adjustments there.

@DPete - A good one. But I have never been able to do tap tempo. Clapping is fine, but put a switch, mouse button or spacebar between me and the beat, and I can't do it.

I put in a feature request some time ago about a variable speed metronome that would allow you to dial-in a tempo. As I recall, nobody gave it a sniff, but I'd still like to see it.

I think it would also help when you try and add a click to something that didn't originally have one. I've tried a number of high tech ways to determine tempo from a live track but a manual metronome with a dial works best for me.

twelvetone
[...] I'm just clapping and singing the song in my head. [...]

If you use a microphone, Shift-M is more useful to me than with a metronome. People will naturally try to synch to something they hear, so the metronome can derail some rather than be a guide (especially for creation and you engage a metronome off by 30 bpm).
 
If you are clapping/singing/humming into a microphone, ever better. When you have a natural feel for it, capture it (no metronome at all), and use shift-M (if you were singing/humming too, you also captured key). You can always fine-tune both of these later on, but that is very quick and easy.