Most of my Tascam mixers had the HP jack right up front where I like them. Since my last one just died I'm now using a Behringer UFX1204 which puts the HP jack all the way at the top where the cord strings across knobs and sliders and gets in the way of my hands. I'm always fighting it.

Though most modern mixers put them there it makes no sense to me and I'd like to relocate it or pig tail a new one to the  front. The lower front panel is about 5/8" x 11" where this could be done. What's the best way to drill an 11/32" hole there?

It's a common annoyance in a lot of gear, done entirely to reduce manufacturing cost because the jack can be mounted on the main circuit board by a machine rather than hand-soldered by an expensive human. I just got a new synth, my first ever with a headphone jack on the front (yay!). I spent 10 minutes searching for the headphone jack on the back panel before it occurred to me to check the front.
 
On a conventional full-size console, there's usually room to wire in a jack at a more convenient location. Unfortunately, compact mixers like yours typically have very little room to spare inside. Your best solution might be to add an inexpensive headphone amp, which could also let you have more than one headphone output

This one actually has 2 jacks and there looks to be enough room up front for one if I can drill the hole carefully. I just need to convince myself it's worth voiding the 3yr warranty.

I would even go as far as to add a HD if I knew how to mod it that way.

You'll find when you take it apart and void your warranty,  ;) that you will have a hard time finding the place to attach the extension wires.
Myself I would use a short TRS cable to a small headphone amp , look at the Rolls stuff as example. Then put that in a convenient place.  Rolls makes passive models but an active multi output headphone amp is a nice tool to have anyway. 

Why not simply add a male to female extension cord that can be routed out of the way to a location you like?

^^^ I like that suggestion best, especially if this mixer is mobile.

ampfixer
Why not simply add a male to female extension cord that can be routed out of the way to a location you like?

That's too easy.  I like doing things the hard & difficult way, tho it may be the way I go until the warranty is no longer needed.

Once you open the case, I suspect space to mount it will be a problem as they tend to cram things up pretty tight inside.  Best to just do what has been suggested and forget about trying to install a front panel jack.