Being limited to only 4 FX slots (2 FX slots pre + 2 post) on the Player and having no morph, perhaps you are like me and make use of a rack/stage and employ an FX slot dedicated to a solo/volume boost or perhaps you do this by morphing. Migrating your rigs to the player often results in a few compromises owning to the limited feature set (which hopefully be expanded in future OK 
) but there is a way...
Here's a work-around that can be applied to Player, Rack/toaster and the Stage alike:
Using midi NRPN, you can assign an external controller to modify your rig volume.
Firstly, you will need to "normalise" your rig-volumes to 0dB and then "compensate" these level adjustment amounts by transferring this amount to the amp-volume parameter (ie if the rig volume is +1dB, set it to 0dB and add 1dB to the the amp-volume parameter to achieve the same output level)
Next, on your external controller (yes- this does require some additional hardware) create midi-data to toggle/send the following midi data on whatever channel applies;
Set rig-volume to +3dB
CC 99 = 4, CC 98 = 1, CC 6 = 80, CC 38 = 0
This equates as-
NRPN Parameter address: MSB = 4, LSB = 1 (the Rig volume parameter)
NRPN Parameter value: MSB = 80, LSB = 0 (a value of +3dB) this could also be a different value between -6dB to +6dB (or whatever the full-range of this parameter is
additionally, you may want this midi data too:
Reset rig-volume to +0dB
CC 99 = 4, CC 98 = 1, CC 6 = 64, CC 38 = 0
This equates as-
NRPN Parameter address: MSB = 4, LSB = 1 (the Rig volume parameter)
NRPN Parameter value: MSB = 80, LSB = 0 (a value of 0dB)
Alternately, calling up a slot will restore its saved values so you may not need the "reset to 0dB" command.
This then gains "solo boosts" without using up any FX slot nor relying on a morphed parameter.
PS- you could also do all of this by employing a volume pedal but that may be something you already have assigned to wah or volume tasks.
PPS- this obviously is dependant on your midi-controller capabilities and understanding how to get it to produce this midi data.
