Chord substitution

consider this scenario. I want to substitute the G7 - as the V of a
2-5-1 progression in C - with a tritone. So I pick a Db7 chord.
When it comes to creating an impro line around this chord. as
a first choice. a lydian Db7 scale? and again what are the scalar possibilities
available. other than the lydian approach?
From G it would read: G Ab Bb B Db Eb F
As you can see it includes the basic root. major third and 7th.
In addition it has altered 5ths. If you check this out you see that if you play these excact notes starting
on the Db. VOILA you have what is known as Lydian flat 7 scale. This is the
one you are referring to.
And what is this if you start on the G? depending on your taste and musical situation. try using both these
altered/lydian flat 7 scales.
it's a symetrical scale. This makes it easy to learn a
fingering. as it will always repeat itself.
It's just half step then whole step then half step etc
From G it gives you the flat 9. Sharp 11 (or flat 5) but it also
gives you the natural major 6 or major 13 if you like this colour better
than the b6 or b13 of the altered scale.

Frode suggested a good approach. But I'm not crazy about using the altered
dominant ALL the time; I think it gets a bit repetitive.
Every major key has ONE V7 chord that is diatonic to the progression - as
does the "harmonized" minor scale.
anytime you play on a V chord. you are ALREADY playing in the key
5 steps down from it. For example. a G7 chord is in the key of Cmaj/min; an
F#7 chord is in Bmaj/min. The maj/min will depend on the other material
being played.
you wish to use a TT substitute for G7. Then for purposes of this approach. you are playing IN the key of
GbMajor at that point - or to look at it another way. as long as you flat
everything except the F. you'll produce all the notes that will wiork with
the Db7.
You WILL need to emphasize the Db as a chord root (and oddly enough. avoid
the Gb on a strong beat). but you are not bound by any pattern dictates or
special scales. To get back to C. just move from the Gb fingering to Cmaj
fingering. If you can play a major scale. If you want to add in some "altered" notes. you don't have to use any
special scales. Try playing the key of F#/Gb MINOR over the Db7. Doing so
will give you the following altered notes on Db7:
To get more altered tones. try superimposing different Maj/min scales over
the chord. There are many different approaches you can use.
you could get by very well just by knowing and applying Maj. and the pentatonic scales.
I know this probably sounds really confusing. but if you sit with it for
awhile and experiment. Conservatives are not necessarily stupid.
but most stupid people are conservatives."
- John Stuart Mill

I only wanted to keep all the notes flat and not mix flats and sharps. This
is most of the time only more confusing. especially when reading parts....