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You can always use a pants stretcher to go up a size.
Congratulations on progress at the gym. I'm having the opposite problem: I'm trying to lose weight at the gym and can't get my stubborn gut to go away. That's one of the cons of working in the craft beer industry.
I’ll Amazon gift this to you so you can get back into your ABU’s: https://www.amazon.com/Pant-Stretcher-Heavy-Instant-Stretch/dp/B00AZNK1RO
A hat stretcher with an extender is sometimes used for this. See here for an example.
Pant Stretcher - Heavy Duty - Easy to Use - Instant Stretch - 30" to 59" Stretch Range https://www.amazon.com/dp/B00AZNK1RO/ref=cm_sw_r_cp_apa_rlecybG38T42C
I've seen others have luck with one of these mate. Might be worth a shot.
The thigh is probably not going to stretch any. If you really want to stretch the waist you can use this. I use one for my unsanforized http://www.amazon.com/Pant-Stretcher-Heavy-Instant-Stretch/dp/B00AZNK1RO